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Re: [regsaudioforum] XTC Function of TacT RCS 2.2XP

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  • Tom Mallin
    P.S. Further experimentation with XTC indicates that the shortcomings at the center of the stage which I made much of are not an inherent problem with XTC. I
    Message 1 of 13 , Aug 1, 2008

      P.S.  Further experimentation with XTC indicates that the shortcomings at the center of the stage which I made much of are not an inherent problem with XTC.  I have now ameliorated those problems to the degree that now I think it is a matter of taste as to whether one would prefer the drier yet more rounded and forward placement of centered soloists provided by ordinary stereo to the more ambient equally focused sound of such soloists through XTC.

       

      I fixed this problem by merely moving my chair back a couple of inches and slightly modifying the XTC settings.  I'm still finding the sound best using algorithm A-1 and .07 milliseconds delay, but am now using a spread factor of 73.  Getting the listening position at just the right spot to yield the correct angular separation between the speakers seems to be very important in my set up.  Not only did the center stage improve, but the tendency of the sides of the soundstage to wrap forward, around to the side, and up is greatly reduced.  Some may like that effect, but it is not what I call "envelopment" since there is no wrap around to the rear as there is with true surround sound.  It just sounds like a U-shaped stage with the center recessed and the sides forward and a bit up.  Moving the listening position back that couple of inches has created a very stable huge wall-to-wall rectangular soundstage from in front of the speakers to the wall behind the speakers.

       

      I am also finding the "brick wall effect" I mentioned to be less and less of an impediment, so great is the clarity and rearward extension of the stage behind the speakers.

       

      I still don't think the stage layout is like one hears live in a hall from even very close up and in that sense is not spatially "natural" in the way ordinary stereo with 90-degree-separated speakers can be with Blumlein recordings, for example.  But even being the purist that I am about such things, I must admit that XTC listening is hugely fun--a gas, in fact--and quite enthralling for its "bigger than life" way with recorded spaces.

       

      One other positive quality of XTC that I did not mention before is the way it separates out and defines musical instruments or lines.  This may be partly a product of the greater spatial "explosion" of the stereo information XTC provides.  You hear musical details more easily.  They seem "uncovered" compared to the ordinary stereo reproduction.  A/B comparisons reveal that these details are there in stereo, but are much more obvious with XTC. 

       

      The downside is that these uncovered musical details are accompanied by a degree of spatial expansion/explosion which is considerably more "pulled apart" than what one hears from any audience perspective in any concert hall I've ever been in.  I recognize that for some listeners this degree of added spatial explosion will not be a "downside" at all, but more of the space you've craved all along.  Whether XTC represents the microphone's viewpoint on things is mere speculation.  I don't think it represents what one hears in a hall if you stand with your ears at the approximate position of a typically close coincident stereo microphone.  I get that kind of perspective on live events from my frequently-first-row seats. 

       

      XTC might represent the type of space captured by widely separated microphones.  Listen to your stereo from the sweet spot while cupping your hands behind your ears.  You will hear many aspects of the reproduced space firm up and expand.  Cupping your hands behind your ears acts to widen the distance between your ears and thus increases the interaural time differences and might also decrease head shadowing.

         

      Anthony Padilla of TacT says that a big electronics retailer is looking hard at the XTC function, presumably for surround sound.  If the equivalent of four-channel Ambiophonics (for true wrap-all-the-way-around envelopment) could be put on an XTC-squared chip inside a reasonably priced home theater receiver, it would put to shame Dolby and DTS surround modes, I think, and would be fully compatible with all two-channel program material.

       

      I keep delaying going back to my normal 90-degree-speaker set up.  I keep telling myself that XTC listening is less natural and that I will tire of the sensational effect soon enough.  That may well be, but for right now, I'm looking for excuses not to change anything.  After all, I can beta test the latest version of the new TacT software with XTC still active, and without actually listening to an equalization-based target curve, right?  :-) 

       



      >>> tmallin@... 7/27/2008 5:40 PM >>>

      XTC Function of TacT RCS 2.2XP

       

      In one of the recent iterations of the firmware updates available for download from the TacT Web site, the XTC function appeared as one of the Menu options.  XTC stands for Cross Talk Cancellation.  (Interesting:  the acronym could just as easily have been CTC or CTX to represent the same phrase.)  Basic information about setting up the XTC function is on the TacT site at:

       

      http://www.tactlab.com/Resources/Downloads/How to setup.htm

       

      Thanks to Les Levanthal for noting on the Real TacT Hackers Forum that more detailed explanations of what is going on here are at:

       

      http://www.ambiophonics.org/Ambiophiles.htm

       

      and

       

      http://www.ambiophonics.org/papers//RG-RACE_AES123NYC0710.pdf

       

      As you can infer from those last two URLs, what is really going on with the XTC function is an implementation of Ralph Glasgal's Ambiophonics system.  TacT has now thrown in Ambiophonics "for free," as it were for owners of the XP version of their processor like me.

       

      I tried XTC briefly when it first became available.  I used it in my usual 90-degree-separation speaker set up.  It sounded weird.  Even after playing with the parameters in various ways, it still sounded weird.  Very phasey with the tugging-at-the-ears effect that phase manipulations often produce with stereo playback.

       

      There it sat for months.  I have seen little comment about the sound of the XTC software on the TacT forums or elsewhere.  Then Les Levanthal recently pointed out to me that the XTC system is meant to implement a two-channel form of the Ambiophonics system and, like Ambiophonics itself, is meant to be implemented in a system where the speakers are separated only by about 20 degrees.

       

      SET UP

       

      For the last couple of days I've been experimenting with the XTC function again, this time in a more appropriately arranged system.  I left my Gradient 1.5s where they were, at 90 degrees of separation.  I moved my Harbeth Monitor 40s back into the dedicated audio room and set them up on my 24"-high Target stools.  The speakers are set up 28" center to center, which means than only about 11" separates the sidewalls of the two speakers.  They are about 80" from the wall behind them and I'm sitting in my Steelcase Leap chair adjusted to maximum height some 80" back from the plane of the speakers and 80" in front of the wall behind me.  Sort of a "rule of thirds" set up.

       

      I had to move further back than my usual 45" from the plane of the speakers since the Harbeths are too wide to yield a 20-degree angle between them from that close up.  Besides, Glasgal recommends a listening distance of two to three meters for Ambiophonics.

       

      As now set up, the Harbeth driver centers are more than 62" from the side walls of my 20' L x 12' 8.5" W x 8' H room.  This can't help but cut way down on destructive side wall reflections compared to my usual set up, which has them only 30.5" from the side walls.

       

      For these preliminary experiments I have not be using any equalization.  This unusual positioning of the Harbeths tames the usual big 60 Hz bass resonance I usually get enough so that, while they sound warm and full, they are not obnoxiously so.

       

      So far I am not using any barrier between the speakers.  A short barrier is shown in current pictures, but it does not extend much, if any, beyond the speakers.  I guess the DSP of the XTC program takes the place of the substantial barrier which extended to near the listener's nose in early analog implementations of the Ambiophonics system.  I have yet to locate any discussion of the current function of the short barrier shown in the pictures I've seen of Glasgal's current set up.

       

      I am using my usual complement of Sonex foam to dampen first and second reflections and a bit more.  Glasgal recommends a lot of room absorption for Ambiophonics set ups.

       

      I have the speakers facing straight ahead, with no toe in, since that is how Glasgal shows his front speakers arranged.  With a 20-degree separation, I am listening 10 degrees off the horizontal axis of the speakers, but on the preferred vertical axis.

       

      An easy way to compute how far to separate the speaker centers to achieve a 20-degree separation between them is to multiply the distance from the plane of the speakers to the listening position by 0.35.  For those familiar with trigonometry, the 0.35 represents two times the tangent of 10 degrees.

       

      PARAMETERS

       

      The XTC screen on the TacT allows you to instantly toggle the XTC software on and off for comparisons.  I daresay that no one will need a blind test to hear the difference between on and off from the listening position.

       

      A choice of 10 cross-talk algorithms is provided, labeled A-1 through A-5 and B-1 through B-5.

       

      The delay time parameter represents the time differences between when sound from each loudspeaker reaches you left versus your right ears.  It is adjustable from 0.2 to 10 milliseconds.

       

      The Spread Factor parameter does just what it sounds like.  It controls the degree of stage spread the software injects.  It is adjustable from zero to 100.

       

      Some simple and some more detailed discussion of these parameters can be found at the links above.

       

      MY FAVORITE SETTINGS

       

      With the speakers and listening position so set up, I preferred:

       

      1.  XTC on to XTC off.  Ya, think?  If I didn't, I wouldn't be writing this.

       

      2.  Algorithms A-1 and B-1 sounded basically the same and best to me.  Some discussion I found suggests that them may be the same.

       

      3.  The Spread Factor sounded best in the 70 to 75 range with 72 being my current favorite.  At more than about 75, the stage began to spread too much of the sound forward, up and to my sides, acting to both recess the center and create a slight lack of center fill.  The subjective reaction to the setting of this factor may well depend on how far the speakers are from the side walls, but I note that I was in the range recommended by TacT.

       

      4.  The delay time parameter was the most difficult for me to set.  Any setting of 0.10 or above sounds awful to me.  At settings higher than that, an extreme nasality and then some type of distortion becomes evident.  At settings below 0.05, the sound becomes a bit rolled off sounding in the highs.  Only the settings of 0.05, 0.06, 0.07, and 0.08 sound listenable to me.  Right now, I think 0.07 is my favorite.  Among these settings there is a trade off between best imaging and staging and most natural tonal balance.

       

      THE SOUND

       

      This is really some parlor trick.  Amazing and spectacular for sure.  In some ways, it's better than ordinary stereo, even my 90-degree-separation variety.  In some other ways, it's not as natural sounding as what I'm used to.  Here are the pros and cons of using the XTC function as I currently see them:

       

                PROS

       

      1.  The obvious:  the widest, deepest stage I've ever heard with the speakers arranged to fire into the long dimension of my room, considerably wider and at least as deep as with my 90-degree-separation set up with the Gradient 1.5s, which, until now, was the widest and deepest.  The contrast in sound when toggling XTC on and off from the sweet spot is astounding.  Off, and there is this very narrow stage with good depth; on some material, it is barely stereo (in left-to-right terms) at all.  With XTC on, zowie!  The stage explodes into hugeness which is all the more remarkable since you can see where the speakers are-basically straight in front of you.

       

      2.  The stage height illusion is greatly enhanced.

       

      3.  Images on the stage seem more rounded and three dimensional.

       

      4.  The above effects seem quite stable for small head movements.  While the effects are at their best in the sweet spot, they are entirely audible and stable when listening direct between the speakers all the way back to the wall behind the listening chair, another 80 inches back.  You can clearly hear the stage expand and collapse when toggling XTC on and off from anywhere in the room (even behind the speakers), but off the center line you only have a vague idea of the improvement.

       

      5.  The system seems able to play louder with less distortion with XTC on.

       

      6.  The bass seems both flatter and more detailed with XTC on, while at the same time seeming stronger.  I know; that sounds contradictory, but that's my subjective impression.

       

      7.  The presentation seems overall "meatier" with a greater sense of "ease" with XTC on.

       

      8.  On certain instruments, especially pianos, there is an apparent reduction in distortion with XTC on.

       

      9.  The speakers disappear more as sound sources.

       

      10.  The system seems to work equally well for recordings miked in various ways.  While some recordings sound more spectacularly enhanced by the toggling on of XTC than others, I haven't really been able to identify the particular aspect of a recording which makes it seem more enhanced than some other with XTC switched on.  XTC seems to enhance all types of recordings in the above-mentioned ways.  Perhaps a closer reading of Glasgal's technical papers would suggest an answer.

       

      11.  All the above effects are equally strong with or without my JL Audio subwoofers in play.  The contrast of just the M40s playing with such little separation between them with XTC off versus the room-filling, much more powerful sound they seem to have with XTC on, just makes me shake my head in wonder.

       

                CONS

       

      1.  With XTC on, centered images sound both less surely centered and less rounded, as well as a bit recessed.  They also sound a bit thin (as in weak in upper bass/lower midrange), nasal, and surrounded with excess reverberation.  This is a serious problem on recordings which rely on centered soloists.  So far, I have found no setting of any of the parameters which avoids this result.  Maybe this is what the short barrier between the speakers helps eliminate. 

       

      Lest you think this is just a matter of the narrow speaker separation giving abnormally strong centered images with XTC off, let me assure you that the Harbeths in my usual set up yield superb centered images even with 90 degree separation and I don't hear anything superior to that with XTC off with the Harbeths spaced close together as they are now.

       

      2.  For all the spatial expansion, I don't get the impression that what I am hearing is as natural in terms of spatial layout as what I normally hear with my 90-degree separated speakers.  More spectacular and mind-boggling, yes, but not as natural.  Perhaps this is why I don't hear a clear differentiation between the effects of XTC on different types of recordings.  The processing seems to create a generic spatial enhancement that tends to overpower the differences usually audible from one type of miking to another.

       

      3.  There are tonal balance changes in the midrange which depend on the setting of the delay time parameter.  I find myself trading off spatial enhancement against these tonal changes, with no one setting seeming totally natural.  Some will undoubtedly find the very lowest settings (0.02 through 0.04) preferable since while a bit dull tonally, and a bit less spatially spectacular, they at least do not interject the occasional nasality or brightness of the higher settings (0.05 through 0.08) which I usually find the most acceptable.

       

      4.  I do not like the visual effect of having the speakers almost directly in front of me.  I tend to listen with my eyes open and use my eyes while listening to focus on the place from which sounds seem to emanate.  Having the speakers directly in front of my eyes distracts me and impedes focusing on images directly behind the speakers.  Thus, despite the fact that less sound seems to emanate from the speakers themselves, the speakers get in their own way a bit, akin to the "brick wall effect" I've mentioned before with respect to walls close behind the speakers and large panel speakers.

       

      In fairness, this effect would be less with small speakers like the Gradients.  And it is a tribute to the XTC software that I still get a great impression of depth even at center stage despite the speakers being right there in front.  Still, this is an aspect where a 90-degree-speaker separation is way ahead:  in such a set up, the speakers are mere anchors to the stage and only in one's peripheral vision most of the time.

       

      BOTTOM LINE:

       

      If you have a TacT RCS 2.2XP, this is definitely worth trying.  Your reaction to the sound may well vary from mine because of different set up or preferences.  However, I think you will surely have a lot of fun experimenting with this, regardless of whether you decide to stick with it or go back to "normal" stereo.

    • Robert Greene
      These things , these digital signal processing alterations of the sound, can be a lot of fun. I have had a Sonic Hologram for years, and somewhere around I
      Message 2 of 13 , Aug 1, 2008
        These things , these digital signal processing alterations of the
        sound, can be a lot of fun. I have had a Sonic Hologram for years,
        and somewhere around I have a Philips processor that lets one
        widen the stereo image by inserting some reverse phase energy(-R
        into L, -L into R) in varying amounts and so on.

        But it seems to me that it is important to realize that ,however
        much fun these things are--and of course there will be more and more
        of them since digital processing with computers is effectively free--
        this has rather little to do with reproducing recordings as they
        were made to be heard.

        I am not saying that the process has been perfect. Lots of things
        about stereo playback have been allowed to "float"(even the angle
        between speakers). But still, the people who made the recordings did
        have something in mind. Applying a lot of processing was not it.

        DSP processing to play with stereo imaging and so on is fun,
        but it is not what one might think of as receiving the message
        intended. DSP to make things accurate is one thing. DSP to change it
        around is mostly just playing games, to my mind. Some of the effects
        might be "musically positive" in some sense of that phrase. But in
        the end, recording and playback is a communication channel. Messing
        about with one end makes it stop being communication and start being
        do it yourself pseudo-creation. It is like Photoshopping a Rembrandt
        or something. It might look better to you or not. But it would not
        be the real thing any longer. There really was a performance there
        and the good recording engineers tried to get it down. It seems to
        me that one probably ought to try to hear it as was intended.

        Of course there is no reason not to have a little fun--except
        perhaps that life is short and one might want to spend the time
        actually listening to music! On the other hand, playing with DSP
        programs is a lot cheaper than playing with audio equipment and
        changing it all the time!

        REG



        --- In regsaudioforum@yahoogroups.com, "Tom Mallin" <tmallin@...>
        wrote:
        >
        >
        > P.S. Further experimentation with XTC indicates that the
        shortcomings at the center of the stage which I made much of are not
        an inherent problem with XTC. I have now ameliorated those problems
        to the degree that now I think it is a matter of taste as to whether
        one would prefer the drier yet more rounded and forward placement of
        centered soloists provided by ordinary stereo to the more ambient
        equally focused sound of such soloists through XTC.
        >
        > I fixed this problem by merely moving my chair back a couple of
        inches and slightly modifying the XTC settings. I'm still finding
        the sound best using algorithm A-1 and .07 milliseconds delay, but
        am now using a spread factor of 73. Getting the listening position
        at just the right spot to yield the correct angular separation
        between the speakers seems to be very important in my set up. Not
        only did the center stage improve, but the tendency of the sides of
        the soundstage to wrap forward, around to the side, and up is
        greatly reduced. Some may like that effect, but it is not what I
        call "envelopment" since there is no wrap around to the rear as
        there is with true surround sound. It just sounds like a U-shaped
        stage with the center recessed and the sides forward and a bit up.
        Moving the listening position back that couple of inches has created
        a very stable huge wall-to-wall rectangular soundstage from in front
        of the speakers to the wall behind the speakers.
        >
        > I am also finding the "brick wall effect" I mentioned to be less
        and less of an impediment, so great is the clarity and rearward
        extension of the stage behind the speakers.
        >
        > I still don't think the stage layout is like one hears live in a
        hall from even very close up and in that sense is not
        spatially "natural" in the way ordinary stereo with 90-degree-
        separated speakers can be with Blumlein recordings, for example.
        But even being the purist that I am about such things, I must admit
        that XTC listening is hugely fun--a gas, in fact--and quite
        enthralling for its "bigger than life" way with recorded spaces.
        >
        > One other positive quality of XTC that I did not mention before is
        the way it separates out and defines musical instruments or lines.
        This may be partly a product of the greater spatial "explosion" of
        the stereo information XTC provides. You hear musical details more
        easily. They seem "uncovered" compared to the ordinary stereo
        reproduction. A/B comparisons reveal that these details are there
        in stereo, but are much more obvious with XTC.
        >
        > The downside is that these uncovered musical details are
        accompanied by a degree of spatial expansion/explosion which is
        considerably more "pulled apart" than what one hears from any
        audience perspective in any concert hall I've ever been in. I
        recognize that for some listeners this degree of added spatial
        explosion will not be a "downside" at all, but more of the space
        you've craved all along. Whether XTC represents the microphone's
        viewpoint on things is mere speculation. I don't think it
        represents what one hears in a hall if you stand with your ears at
        the approximate position of a typically close coincident stereo
        microphone. I get that kind of perspective on live events from my
        frequently-first-row seats.
        >
        > XTC might represent the type of space captured by widely separated
        microphones. Listen to your stereo from the sweet spot while
        cupping your hands behind your ears. You will hear many aspects of
        the reproduced space firm up and expand. Cupping your hands behind
        your ears acts to widen the distance between your ears and thus
        increases the interaural time differences and might also decrease
        head shadowing.
        >
        > Anthony Padilla of TacT says that a big electronics retailer is
        looking hard at the XTC function, presumably for surround sound. If
        the equivalent of four-channel Ambiophonics (for true wrap-all-the-
        way-around envelopment) could be put on an XTC-squared chip inside a
        reasonably priced home theater receiver, it would put to shame Dolby
        and DTS surround modes, I think, and would be fully compatible with
        all two-channel program material.
        >
        > I keep delaying going back to my normal 90-degree-speaker set up.
        I keep telling myself that XTC listening is less natural and that I
        will tire of the sensational effect soon enough. That may well be,
        but for right now, I'm looking for excuses not to change anything.
        After all, I can beta test the latest version of the new TacT
        software with XTC still active, and without actually listening to an
        equalization-based target curve, right? :-)
        >
        >
        > >>> tmallin@... 7/27/2008 5:40 PM >>>
        >
        > XTC Function of TacT RCS 2.2XP
        >
        > In one of the recent iterations of the firmware updates available
        for download from the TacT Web site, the XTC function appeared as
        one of the Menu options. XTC stands for Cross Talk Cancellation.
        (Interesting: the acronym could just as easily have been CTC or CTX
        to represent the same phrase.) Basic information about setting up
        the XTC function is on the TacT site at:
        >
        > http://www.tactlab.com/Resources/Downloads/How to setup.htm (
        http://www.tactlab.com/Resources/Downloads/How%20to%20setup.htm )
        >
        > Thanks to Les Levanthal for noting on the Real TacT Hackers Forum
        that more detailed explanations of what is going on here are at:
        >
        > http://www.ambiophonics.org/Ambiophiles.htm
        >
        > and
        >
        > http://www.ambiophonics.org/papers//RG-RACE_AES123NYC0710.pdf (
        http://www.ambiophonics.org/papers/RG-RACE_AES123NYC0710.pdf )
        >
        > As you can infer from those last two URLs, what is really going on
        with the XTC function is an implementation of Ralph Glasgal's
        Ambiophonics system. TacT has now thrown in Ambiophonics "for
        free," as it were for owners of the XP version of their processor
        like me.
        >
        > I tried XTC briefly when it first became available. I used it in
        my usual 90-degree-separation speaker set up. It sounded weird.
        Even after playing with the parameters in various ways, it still
        sounded weird. Very phasey with the tugging-at-the-ears effect that
        phase manipulations often produce with stereo playback.
        >
        > There it sat for months. I have seen little comment about the
        sound of the XTC software on the TacT forums or elsewhere. Then Les
        Levanthal recently pointed out to me that the XTC system is meant to
        implement a two-channel form of the Ambiophonics system and, like
        Ambiophonics itself, is meant to be implemented in a system where
        the speakers are separated only by about 20 degrees.
        >
        > SET UP
        >
        > For the last couple of days I've been experimenting with the XTC
        function again, this time in a more appropriately arranged system.
        I left my Gradient 1.5s where they were, at 90 degrees of
        separation. I moved my Harbeth Monitor 40s back into the dedicated
        audio room and set them up on my 24"-high Target stools. The
        speakers are set up 28" center to center, which means than only
        about 11" separates the sidewalls of the two speakers. They are
        about 80" from the wall behind them and I'm sitting in my Steelcase
        Leap chair adjusted to maximum height some 80" back from the plane
        of the speakers and 80" in front of the wall behind me. Sort of
        a "rule of thirds" set up.
        >
        > I had to move further back than my usual 45" from the plane of the
        speakers since the Harbeths are too wide to yield a 20-degree angle
        between them from that close up. Besides, Glasgal recommends a
        listening distance of two to three meters for Ambiophonics.
        >
        > As now set up, the Harbeth driver centers are more than 62" from
        the side walls of my 20' L x 12' 8.5" W x 8' H room. This can't
        help but cut way down on destructive side wall reflections compared
        to my usual set up, which has them only 30.5" from the side walls.
        >
        > For these preliminary experiments I have not be using any
        equalization. This unusual positioning of the Harbeths tames the
        usual big 60 Hz bass resonance I usually get enough so that, while
        they sound warm and full, they are not obnoxiously so.
        >
        > So far I am not using any barrier between the speakers. A short
        barrier is shown in current pictures, but it does not extend much,
        if any, beyond the speakers. I guess the DSP of the XTC program
        takes the place of the substantial barrier which extended to near
        the listener's nose in early analog implementations of the
        Ambiophonics system. I have yet to locate any discussion of the
        current function of the short barrier shown in the pictures I've
        seen of Glasgal's current set up.
        >
        > I am using my usual complement of Sonex foam to dampen first and
        second reflections and a bit more. Glasgal recommends a lot of room
        absorption for Ambiophonics set ups.
        >
        > I have the speakers facing straight ahead, with no toe in, since
        that is how Glasgal shows his front speakers arranged. With a 20-
        degree separation, I am listening 10 degrees off the horizontal axis
        of the speakers, but on the preferred vertical axis.
        >
        > An easy way to compute how far to separate the speaker centers to
        achieve a 20-degree separation between them is to multiply the
        distance from the plane of the speakers to the listening position by
        0.35. For those familiar with trigonometry, the 0.35 represents two
        times the tangent of 10 degrees.
        >
        > PARAMETERS
        >
        > The XTC screen on the TacT allows you to instantly toggle the XTC
        software on and off for comparisons. I daresay that no one will
        need a blind test to hear the difference between on and off from the
        listening position.
        >
        > A choice of 10 cross-talk algorithms is provided, labeled A-1
        through A-5 and B-1 through B-5.
        >
        > The delay time parameter represents the time differences between
        when sound from each loudspeaker reaches you left versus your right
        ears. It is adjustable from 0.2 to 10 milliseconds.
        >
        > The Spread Factor parameter does just what it sounds like. It
        controls the degree of stage spread the software injects. It is
        adjustable from zero to 100.
        >
        > Some simple and some more detailed discussion of these parameters
        can be found at the links above.
        >
        > MY FAVORITE SETTINGS
        >
        > With the speakers and listening position so set up, I preferred:
        >
        > 1. XTC on to XTC off. Ya, think? If I didn't, I wouldn't be
        writing this.
        >
        > 2. Algorithms A-1 and B-1 sounded basically the same and best to
        me. Some discussion I found suggests that them may be the same.
        >
        > 3. The Spread Factor sounded best in the 70 to 75 range with 72
        being my current favorite. At more than about 75, the stage began
        to spread too much of the sound forward, up and to my sides, acting
        to both recess the center and create a slight lack of center fill.
        The subjective reaction to the setting of this factor may well
        depend on how far the speakers are from the side walls, but I note
        that I was in the range recommended by TacT.
        >
        > 4. The delay time parameter was the most difficult for me to
        set. Any setting of 0.10 or above sounds awful to me. At settings
        higher than that, an extreme nasality and then some type of
        distortion becomes evident. At settings below 0.05, the sound
        becomes a bit rolled off sounding in the highs. Only the settings
        of 0.05, 0.06, 0.07, and 0.08 sound listenable to me. Right now, I
        think 0.07 is my favorite. Among these settings there is a trade
        off between best imaging and staging and most natural tonal balance.
        >
        > THE SOUND
        >
        > This is really some parlor trick. Amazing and spectacular for
        sure. In some ways, it's better than ordinary stereo, even my 90-
        degree-separation variety. In some other ways, it's not as natural
        sounding as what I'm used to. Here are the pros and cons of using
        the XTC function as I currently see them:
        >
        > PROS
        >
        > 1. The obvious: the widest, deepest stage I've ever heard with
        the speakers arranged to fire into the long dimension of my room,
        considerably wider and at least as deep as with my 90-degree-
        separation set up with the Gradient 1.5s, which, until now, was the
        widest and deepest. The contrast in sound when toggling XTC on and
        off from the sweet spot is astounding. Off, and there is this very
        narrow stage with good depth; on some material, it is barely stereo
        (in left-to-right terms) at all. With XTC on, zowie! The stage
        explodes into hugeness which is all the more remarkable since you
        can see where the speakers are-basically straight in front of you.
        >
        > 2. The stage height illusion is greatly enhanced.
        >
        > 3. Images on the stage seem more rounded and three dimensional.
        >
        > 4. The above effects seem quite stable for small head movements.
        While the effects are at their best in the sweet spot, they are
        entirely audible and stable when listening direct between the
        speakers all the way back to the wall behind the listening chair,
        another 80 inches back. You can clearly hear the stage expand and
        collapse when toggling XTC on and off from anywhere in the room
        (even behind the speakers), but off the center line you only have a
        vague idea of the improvement.
        >
        > 5. The system seems able to play louder with less distortion with
        XTC on.
        >
        > 6. The bass seems both flatter and more detailed with XTC on,
        while at the same time seeming stronger. I know; that sounds
        contradictory, but that's my subjective impression.
        >
        > 7. The presentation seems overall "meatier" with a greater sense
        of "ease" with XTC on.
        >
        > 8. On certain instruments, especially pianos, there is an
        apparent reduction in distortion with XTC on.
        >
        > 9. The speakers disappear more as sound sources.
        >
        > 10. The system seems to work equally well for recordings miked in
        various ways. While some recordings sound more spectacularly
        enhanced by the toggling on of XTC than others, I haven't really
        been able to identify the particular aspect of a recording which
        makes it seem more enhanced than some other with XTC switched on.
        XTC seems to enhance all types of recordings in the above-mentioned
        ways. Perhaps a closer reading of Glasgal's technical papers would
        suggest an answer.
        >
        > 11. All the above effects are equally strong with or without my
        JL Audio subwoofers in play. The contrast of just the M40s playing
        with such little separation between them with XTC off versus the
        room-filling, much more powerful sound they seem to have with XTC
        on, just makes me shake my head in wonder.
        >
        > CONS
        >
        > 1. With XTC on, centered images sound both less surely centered
        and less rounded, as well as a bit recessed. They also sound a bit
        thin (as in weak in upper bass/lower midrange), nasal, and
        surrounded with excess reverberation. This is a serious problem on
        recordings which rely on centered soloists. So far, I have found no
        setting of any of the parameters which avoids this result. Maybe
        this is what the short barrier between the speakers helps
        eliminate.
        >
        > Lest you think this is just a matter of the narrow speaker
        separation giving abnormally strong centered images with XTC off,
        let me assure you that the Harbeths in my usual set up yield superb
        centered images even with 90 degree separation and I don't hear
        anything superior to that with XTC off with the Harbeths spaced
        close together as they are now.
        >
        > 2. For all the spatial expansion, I don't get the impression that
        what I am hearing is as natural in terms of spatial layout as what I
        normally hear with my 90-degree separated speakers. More
        spectacular and mind-boggling, yes, but not as natural. Perhaps
        this is why I don't hear a clear differentiation between the effects
        of XTC on different types of recordings. The processing seems to
        create a generic spatial enhancement that tends to overpower the
        differences usually audible from one type of miking to another.
        >
        > 3. There are tonal balance changes in the midrange which depend
        on the setting of the delay time parameter. I find myself trading
        off spatial enhancement against these tonal changes, with no one
        setting seeming totally natural. Some will undoubtedly find the
        very lowest settings (0.02 through 0.04) preferable since while a
        bit dull tonally, and a bit less spatially spectacular, they at
        least do not interject the occasional nasality or brightness of the
        higher settings (0.05 through 0.08) which I usually find the most
        acceptable.
        >
        > 4. I do not like the visual effect of having the speakers almost
        directly in front of me. I tend to listen with my eyes open and use
        my eyes while listening to focus on the place from which sounds seem
        to emanate. Having the speakers directly in front of my eyes
        distracts me and impedes focusing on images directly behind the
        speakers. Thus, despite the fact that less sound seems to emanate
        from the speakers themselves, the speakers get in their own way a
        bit, akin to the "brick wall effect" I've mentioned before with
        respect to walls close behind the speakers and large panel speakers.
        >
        > In fairness, this effect would be less with small speakers like
        the Gradients. And it is a tribute to the XTC software that I still
        get a great impression of depth even at center stage despite the
        speakers being right there in front. Still, this is an aspect where
        a 90-degree-speaker separation is way ahead: in such a set up, the
        speakers are mere anchors to the stage and only in one's peripheral
        vision most of the time.
        >
        > BOTTOM LINE:
        >
        > If you have a TacT RCS 2.2XP, this is definitely worth trying.
        Your reaction to the sound may well vary from mine because of
        different set up or preferences. However, I think you will surely
        have a lot of fun experimenting with this, regardless of whether you
        decide to stick with it or go back to "normal" stereo.
        >
      • Hugh Pyle
        I believe the original work behind the TacT s crosstalk canceller is the stereo dipole system from Southampton ( http://www.isvr.soton.ac.uk/FDAG/VAP/). It
        Message 3 of 13 , Aug 1, 2008
          I believe the original work behind the TacT's crosstalk canceller is the "stereo dipole" system from Southampton (http://www.isvr.soton.ac.uk/FDAG/VAP/).  It "works", in the sense of accuractely reproducing the stereo soundfield's characteristics (source positioning), at least as well as classic 90-degree stereo speaker separation.  In some ways it works even better -- timbral accuracy across the stage width is quite good.
           
          Personally I don't like it for living-room use because I find its tradeoffs unacceptable.  While there's good image stability with head rotation and along the median line, the image completely falls apart very rapidly with sideways movement, and collapses into a very flat single-speaker-like presentation.  (Traditional stereo of course also falls down for non-centered listeners.  But it doesn't fail as quickly or as badly).
           
          The full-on "Ambiophonic" stuff -- with multiple speakers running synthesised hall reverberation -- is another matter altogether, and seems to me totally artificial... :-)

          On Fri, Aug 1, 2008 at 8:34 PM, Robert Greene <regonaudio@...> wrote:

          These things , these digital signal processing alterations of the
          sound, can be a lot of fun. I have had a Sonic Hologram for years,
          and somewhere around I have a Philips processor that lets one
          widen the stereo image by inserting some reverse phase energy(-R
          into L, -L into R) in varying amounts and so on.

          But it seems to me that it is important to realize that ,however
          much fun these things are--and of course there will be more and more
          of them since digital processing with computers is effectively free--
          this has rather little to do with reproducing recordings as they
          were made to be heard.

          I am not saying that the process has been perfect. Lots of things
          about stereo playback have been allowed to "float"(even the angle
          between speakers). But still, the people who made the recordings did
          have something in mind. Applying a lot of processing was not it.

          DSP processing to play with stereo imaging and so on is fun,
          but it is not what one might think of as receiving the message
          intended. DSP to make things accurate is one thing. DSP to change it
          around is mostly just playing games, to my mind. Some of the effects
          might be "musically positive" in some sense of that phrase. But in
          the end, recording and playback is a communication channel. Messing
          about with one end makes it stop being communication and start being
          do it yourself pseudo-creation. It is like Photoshopping a Rembrandt
          or something. It might look better to you or not. But it would not
          be the real thing any longer. There really was a performance there
          and the good recording engineers tried to get it down. It seems to
          me that one probably ought to try to hear it as was intended.

          Of course there is no reason not to have a little fun--except
          perhaps that life is short and one might want to spend the time
          actually listening to music! On the other hand, playing with DSP
          programs is a lot cheaper than playing with audio equipment and
          changing it all the time!



          REG

          --- In regsaudioforum@yahoogroups.com, "Tom Mallin" <tmallin@...>
          wrote:
          >
          >
          > P.S. Further experimentation with XTC indicates that the
          shortcomings at the center of the stage which I made much of are not
          an inherent problem with XTC. I have now ameliorated those problems
          to the degree that now I think it is a matter of taste as to whether
          one would prefer the drier yet more rounded and forward placement of
          centered soloists provided by ordinary stereo to the more ambient
          equally focused sound of such soloists through XTC.
          >
          > I fixed this problem by merely moving my chair back a couple of
          inches and slightly modifying the XTC settings. I'm still finding
          the sound best using algorithm A-1 and .07 milliseconds delay, but
          am now using a spread factor of 73. Getting the listening position
          at just the right spot to yield the correct angular separation
          between the speakers seems to be very important in my set up. Not
          only did the center stage improve, but the tendency of the sides of
          the soundstage to wrap forward, around to the side, and up is
          greatly reduced. Some may like that effect, but it is not what I
          call "envelopment" since there is no wrap around to the rear as
          there is with true surround sound. It just sounds like a U-shaped
          stage with the center recessed and the sides forward and a bit up.
          Moving the listening position back that couple of inches has created
          a very stable huge wall-to-wall rectangular soundstage from in front
          of the speakers to the wall behind the speakers.
          >
          > I am also finding the "brick wall effect" I mentioned to be less
          and less of an impediment, so great is the clarity and rearward
          extension of the stage behind the speakers.
          >
          > I still don't think the stage layout is like one hears live in a
          hall from even very close up and in that sense is not
          spatially "natural" in the way ordinary stereo with 90-degree-
          separated speakers can be with Blumlein recordings, for example.
          But even being the purist that I am about such things, I must admit
          that XTC listening is hugely fun--a gas, in fact--and quite
          enthralling for its "bigger than life" way with recorded spaces.
          >
          > One other positive quality of XTC that I did not mention before is
          the way it separates out and defines musical instruments or lines.
          This may be partly a product of the greater spatial "explosion" of
          the stereo information XTC provides. You hear musical details more
          easily. They seem "uncovered" compared to the ordinary stereo
          reproduction. A/B comparisons reveal that these details are there
          in stereo, but are much more obvious with XTC.
          >
          > The downside is that these uncovered musical details are
          accompanied by a degree of spatial expansion/explosion which is
          considerably more "pulled apart" than what one hears from any
          audience perspective in any concert hall I've ever been in. I
          recognize that for some listeners this degree of added spatial
          explosion will not be a "downside" at all, but more of the space
          you've craved all along. Whether XTC represents the microphone's
          viewpoint on things is mere speculation. I don't think it
          represents what one hears in a hall if you stand with your ears at
          the approximate position of a typically close coincident stereo
          microphone. I get that kind of perspective on live events from my
          frequently-first-row seats.
          >
          > XTC might represent the type of space captured by widely separated
          microphones. Listen to your stereo from the sweet spot while
          cupping your hands behind your ears. You will hear many aspects of
          the reproduced space firm up and expand. Cupping your hands behind
          your ears acts to widen the distance between your ears and thus
          increases the interaural time differences and might also decrease
          head shadowing.
          >
          > Anthony Padilla of TacT says that a big electronics retailer is
          looking hard at the XTC function, presumably for surround sound. If
          the equivalent of four-channel Ambiophonics (for true wrap-all-the-
          way-around envelopment) could be put on an XTC-squared chip inside a
          reasonably priced home theater receiver, it would put to shame Dolby
          and DTS surround modes, I think, and would be fully compatible with
          all two-channel program material.
          >
          > I keep delaying going back to my normal 90-degree-speaker set up.
          I keep telling myself that XTC listening is less natural and that I
          will tire of the sensational effect soon enough. That may well be,
          but for right now, I'm looking for excuses not to change anything.
          After all, I can beta test the latest version of the new TacT
          software with XTC still active, and without actually listening to an
          equalization-based target curve, right? :-)
          >
          >
          > >>> tmallin@... 7/27/2008 5:40 PM >>>

          >
          > XTC Function of TacT RCS 2.2XP
          >
          > In one of the recent iterations of the firmware updates available
          for download from the TacT Web site, the XTC function appeared as
          one of the Menu options. XTC stands for Cross Talk Cancellation.
          (Interesting: the acronym could just as easily have been CTC or CTX
          to represent the same phrase.) Basic information about setting up
          the XTC function is on the TacT site at:
          >
          > http://www.tactlab.com/Resources/Downloads/How to setup.htm (
          http://www.tactlab.com/Resources/Downloads/How%20to%20setup.htm )

          >
          > Thanks to Les Levanthal for noting on the Real TacT Hackers Forum
          that more detailed explanations of what is going on here are at:
          >
          > http://www.ambiophonics.org/Ambiophiles.htm
          >
          > and
          >
          > http://www.ambiophonics.org/papers//RG-RACE_AES123NYC0710.pdf (
          http://www.ambiophonics.org/papers/RG-RACE_AES123NYC0710.pdf )
          >
          > As you can infer from those last two URLs, what is really going on
          with the XTC function is an implementation of Ralph Glasgal's
          Ambiophonics system. TacT has now thrown in Ambiophonics "for
          free," as it were for owners of the XP version of their processor
          like me.
          >
          > I tried XTC briefly when it first became available. I used it in
          my usual 90-degree-separation speaker set up. It sounded weird.
          Even after playing with the parameters in various ways, it still
          sounded weird. Very phasey with the tugging-at-the-ears effect that
          phase manipulations often produce with stereo playback.
          >
          > There it sat for months. I have seen little comment about the
          sound of the XTC software on the TacT forums or elsewhere. Then Les
          Levanthal recently pointed out to me that the XTC system is meant to
          implement a two-channel form of the Ambiophonics system and, like
          Ambiophonics itself, is meant to be implemented in a system where
          the speakers are separated only by about 20 degrees.
          >
          > SET UP
          >
          > For the last couple of days I've been experimenting with the XTC
          function again, this time in a more appropriately arranged system.
          I left my Gradient 1.5s where they were, at 90 degrees of
          separation. I moved my Harbeth Monitor 40s back into the dedicated
          audio room and set them up on my 24"-high Target stools. The
          speakers are set up 28" center to center, which means than only
          about 11" separates the sidewalls of the two speakers. They are
          about 80" from the wall behind them and I'm sitting in my Steelcase
          Leap chair adjusted to maximum height some 80" back from the plane
          of the speakers and 80" in front of the wall behind me. Sort of
          a "rule of thirds" set up.
          >
          > I had to move further back than my usual 45" from the plane of the
          speakers since the Harbeths are too wide to yield a 20-degree angle
          between them from that close up. Besides, Glasgal recommends a
          listening distance of two to three meters for Ambiophonics.
          >
          > As now set up, the Harbeth driver centers are more than 62" from
          the side walls of my 20' L x 12' 8.5" W x 8' H room. This can't
          help but cut way down on destructive side wall reflections compared
          to my usual set up, which has them only 30.5" from the side walls.
          >
          > For these preliminary experiments I have not be using any
          equalization. This unusual positioning of the Harbeths tames the
          usual big 60 Hz bass resonance I usually get enough so that, while
          they sound warm and full, they are not obnoxiously so.
          >
          > So far I am not using any barrier between the speakers. A short
          barrier is shown in current pictures, but it does not extend much,
          if any, beyond the speakers. I guess the DSP of the XTC program
          takes the place of the substantial barrier which extended to near
          the listener's nose in early analog implementations of the
          Ambiophonics system. I have yet to locate any discussion of the
          current function of the short barrier shown in the pictures I've
          seen of Glasgal's current set up.
          >
          > I am using my usual complement of Sonex foam to dampen first and
          second reflections and a bit more. Glasgal recommends a lot of room
          absorption for Ambiophonics set ups.
          >
          > I have the speakers facing straight ahead, with no toe in, since
          that is how Glasgal shows his front speakers arranged. With a 20-
          degree separation, I am listening 10 degrees off the horizontal axis
          of the speakers, but on the preferred vertical axis.
          >
          > An easy way to compute how far to separate the speaker centers to
          achieve a 20-degree separation between them is to multiply the
          distance from the plane of the speakers to the listening position by
          0.35. For those familiar with trigonometry, the 0.35 represents two
          times the tangent of 10 degrees.
          >
          > PARAMETERS
          >
          > The XTC screen on the TacT allows you to instantly toggle the XTC
          software on and off for comparisons. I daresay that no one will
          need a blind test to hear the difference between on and off from the
          listening position.
          >
          > A choice of 10 cross-talk algorithms is provided, labeled A-1
          through A-5 and B-1 through B-5.
          >
          > The delay time parameter represents the time differences between
          when sound from each loudspeaker reaches you left versus your right
          ears. It is adjustable from 0.2 to 10 milliseconds.
          >
          > The Spread Factor parameter does just what it sounds like. It
          controls the degree of stage spread the software injects. It is
          adjustable from zero to 100.
          >
          > Some simple and some more detailed discussion of these parameters
          can be found at the links above.
          >
          > MY FAVORITE SETTINGS
          >
          > With the speakers and listening position so set up, I preferred:
          >
          > 1. XTC on to XTC off. Ya, think? If I didn't, I wouldn't be
          writing this.
          >
          > 2. Algorithms A-1 and B-1 sounded basically the same and best to
          me. Some discussion I found suggests that them may be the same.
          >
          > 3. The Spread Factor sounded best in the 70 to 75 range with 72
          being my current favorite. At more than about 75, the stage began
          to spread too much of the sound forward, up and to my sides, acting
          to both recess the center and create a slight lack of center fill.
          The subjective reaction to the setting of this factor may well
          depend on how far the speakers are from the side walls, but I note
          that I was in the range recommended by TacT.
          >
          > 4. The delay time parameter was the most difficult for me to
          set. Any setting of 0.10 or above sounds awful to me. At settings
          higher than that, an extreme nasality and then some type of
          distortion becomes evident. At settings below 0.05, the sound
          becomes a bit rolled off sounding in the highs. Only the settings
          of 0.05, 0.06, 0.07, and 0.08 sound listenable to me. Right now, I
          think 0.07 is my favorite. Among these settings there is a trade
          off between best imaging and staging and most natural tonal balance.
          >
          > THE SOUND
          >
          > This is really some parlor trick. Amazing and spectacular for
          sure. In some ways, it's better than ordinary stereo, even my 90-
          degree-separation variety. In some other ways, it's not as natural
          sounding as what I'm used to. Here are the pros and cons of using
          the XTC function as I currently see them:
          >
          > PROS
          >
          > 1. The obvious: the widest, deepest stage I've ever heard with
          the speakers arranged to fire into the long dimension of my room,
          considerably wider and at least as deep as with my 90-degree-
          separation set up with the Gradient 1.5s, which, until now, was the
          widest and deepest. The contrast in sound when toggling XTC on and
          off from the sweet spot is astounding. Off, and there is this very
          narrow stage with good depth; on some material, it is barely stereo
          (in left-to-right terms) at all. With XTC on, zowie! The stage
          explodes into hugeness which is all the more remarkable since you
          can see where the speakers are-basically straight in front of you.
          >
          > 2. The stage height illusion is greatly enhanced.
          >
          > 3. Images on the stage seem more rounded and three dimensional.
          >
          > 4. The above effects seem quite stable for small head movements.
          While the effects are at their best in the sweet spot, they are
          entirely audible and stable when listening direct between the
          speakers all the way back to the wall behind the listening chair,
          another 80 inches back. You can clearly hear the stage expand and
          collapse when toggling XTC on and off from anywhere in the room
          (even behind the speakers), but off the center line you only have a
          vague idea of the improvement.
          >
          > 5. The system seems able to play louder with less distortion with
          XTC on.
          >
          > 6. The bass seems both flatter and more detailed with XTC on,
          while at the same time seeming stronger. I know; that sounds
          contradictory, but that's my subjective impression.
          >
          > 7. The presentation seems overall "meatier" with a greater sense
          of "ease" with XTC on.
          >
          > 8. On certain instruments, especially pianos, there is an
          apparent reduction in distortion with XTC on.
          >
          > 9. The speakers disappear more as sound sources.
          >
          > 10. The system seems to work equally well for recordings miked in
          various ways. While some recordings sound more spectacularly
          enhanced by the toggling on of XTC than others, I haven't really
          been able to identify the particular aspect of a recording which
          makes it seem more enhanced than some other with XTC switched on.
          XTC seems to enhance all types of recordings in the above-mentioned
          ways. Perhaps a closer reading of Glasgal's technical papers would
          suggest an answer.
          >
          > 11. All the above effects are equally strong with or without my
          JL Audio subwoofers in play. The contrast of just the M40s playing
          with such little separation between them with XTC off versus the
          room-filling, much more powerful sound they seem to have with XTC
          on, just makes me shake my head in wonder.
          >
          > CONS
          >
          > 1. With XTC on, centered images sound both less surely centered
          and less rounded, as well as a bit recessed. They also sound a bit
          thin (as in weak in upper bass/lower midrange), nasal, and
          surrounded with excess reverberation. This is a serious problem on
          recordings which rely on centered soloists. So far, I have found no
          setting of any of the parameters which avoids this result. Maybe
          this is what the short barrier between the speakers helps
          eliminate.
          >
          > Lest you think this is just a matter of the narrow speaker
          separation giving abnormally strong centered images with XTC off,
          let me assure you that the Harbeths in my usual set up yield superb
          centered images even with 90 degree separation and I don't hear
          anything superior to that with XTC off with the Harbeths spaced
          close together as they are now.
          >
          > 2. For all the spatial expansion, I don't get the impression that
          what I am hearing is as natural in terms of spatial layout as what I
          normally hear with my 90-degree separated speakers. More
          spectacular and mind-boggling, yes, but not as natural. Perhaps
          this is why I don't hear a clear differentiation between the effects
          of XTC on different types of recordings. The processing seems to
          create a generic spatial enhancement that tends to overpower the
          differences usually audible from one type of miking to another.
          >
          > 3. There are tonal balance changes in the midrange which depend
          on the setting of the delay time parameter. I find myself trading
          off spatial enhancement against these tonal changes, with no one
          setting seeming totally natural. Some will undoubtedly find the
          very lowest settings (0.02 through 0.04) preferable since while a
          bit dull tonally, and a bit less spatially spectacular, they at
          least do not interject the occasional nasality or brightness of the
          higher settings (0.05 through 0.08) which I usually find the most
          acceptable.
          >
          > 4. I do not like the visual effect of having the speakers almost
          directly in front of me. I tend to listen with my eyes open and use
          my eyes while listening to focus on the place from which sounds seem
          to emanate. Having the speakers directly in front of my eyes
          distracts me and impedes focusing on images directly behind the
          speakers. Thus, despite the fact that less sound seems to emanate
          from the speakers themselves, the speakers get in their own way a
          bit, akin to the "brick wall effect" I've mentioned before with
          respect to walls close behind the speakers and large panel speakers.
          >
          > In fairness, this effect would be less with small speakers like
          the Gradients. And it is a tribute to the XTC software that I still
          get a great impression of depth even at center stage despite the
          speakers being right there in front. Still, this is an aspect where
          a 90-degree-speaker separation is way ahead: in such a set up, the
          speakers are mere anchors to the stage and only in one's peripheral
          vision most of the time.
          >
          > BOTTOM LINE:
          >
          > If you have a TacT RCS 2.2XP, this is definitely worth trying.
          Your reaction to the sound may well vary from mine because of
          different set up or preferences. However, I think you will surely
          have a lot of fun experimenting with this, regardless of whether you
          decide to stick with it or go back to "normal" stereo.
          >


        • hoganbo
          Have you or REG heard the XTC Function of TacT RCS 2.2XP? I believe the original work behind the TacT s crosstalk canceller is the stereo dipole system from
          Message 4 of 13 , Aug 1, 2008
            Have you or REG heard the XTC Function of TacT RCS 2.2XP?


            I believe the original work behind the TacT's crosstalk canceller is
            the "stereo dipole" system from Southampton
            (http://www.isvr.soton.ac.uk/FDAG/VAP/). It "works", in the sense of
            accuractely reproducing the stereo soundfield's characteristics
            (source positioning), at least as well as classic 90-degree stereo
            speaker separation. In some ways it works even better -- timbral
            accuracy across the stage width is quite good.

            Personally I don't like it for living-room use because I find its
            tradeoffs unacceptable. While there's good image stability with head
            rotation and along the median line, the image completely falls apart
            very rapidly with sideways movement, and collapses into a very flat
            single-speaker-like presentation. (Traditional stereo of course also
            falls down for non-centered listeners. But it doesn't fail as
            quickly or as badly).

            The full-on "Ambiophonic" stuff -- with multiple speakers running
            synthesised hall reverberation -- is another matter altogether, and
            seems to me totally artificial... :-)
          • Hugh Pyle
            Not exactly: I ve heard RACE on AudioMulch (briefly - I didn t give it any critical listening) as well as the Choueiri stereo-dipole crosstalk filters (basis
            Message 5 of 13 , Aug 2, 2008
              Not exactly: I've heard RACE on AudioMulch (briefly - I didn't give it any critical listening) as well as the Choueiri stereo-dipole crosstalk filters (basis for my comments below).

              On Fri, Aug 1, 2008 at 11:29 PM, hoganbo <hoganbo@...> wrote:

              Have you or REG heard the XTC Function of TacT RCS 2.2XP?


              I believe the original work behind the TacT's crosstalk canceller is
              the "stereo dipole" system from Southampton
              (http://www.isvr.soton.ac.uk/FDAG/VAP/). It "works", in the sense of
              accuractely reproducing the stereo soundfield's characteristics
              (source positioning), at least as well as classic 90-degree stereo
              speaker separation. In some ways it works even better -- timbral
              accuracy across the stage width is quite good.

              Personally I don't like it for living-room use because I find its
              tradeoffs unacceptable. While there's good image stability with head
              rotation and along the median line, the image completely falls apart
              very rapidly with sideways movement, and collapses into a very flat
              single-speaker-like presentation. (Traditional stereo of course also
              falls down for non-centered listeners. But it doesn't fail as
              quickly or as badly).

              The full-on "Ambiophonic" stuff -- with multiple speakers running
              synthesised hall reverberation -- is another matter altogether, and
              seems to me totally artificial... :-)


            • Jose Ramos
              Hi Robert ... more ... - ... With respect, are you perhaps not missing the point about systems such as Ambiophonics? The developers of these systems would
              Message 6 of 13 , Aug 3, 2008
                Hi Robert

                --- In regsaudioforum@yahoogroups.com, "Robert Greene"
                <regonaudio@...> wrote:
                > But it seems to me that it is important to realize that ,however
                > much fun these things are--and of course there will be more and
                more
                > of them since digital processing with computers is effectively free-
                -
                > this has rather little to do with reproducing recordings as they
                > were made to be heard.

                With respect, are you perhaps not missing the point about systems
                such as Ambiophonics? The developers of these systems would argue
                that their whole aim is to in fact recreate the original sound of the
                recording by eliminating the problems of playback in a stereo system
                in the home environment. This is different to playing around with
                the sound to create effects, however pleasing, that are not true to
                the original. Examples of the latter would include DSP hall-effects,
                multichannel from stereo etc.

                I am a long-time Tact RCS user and have listened to the XTC function
                which I do not particularly like in that it does not recreate a sense
                of the original recording IMO - BUT I have not used it correctly as I
                have not set up my speakers close together as is required. I thus
                reserve any judgement about the efficacy of XTC to recreate the
                original sound and defer to the findings of others such as Tom who
                has actually implemented it properly.
                I have heard the XTC properly set up at the 2007 NY HES and at Ralph
                Glasgals home - in these setups, I was impressed by what XTC could do
                and did feel that I was hearing sound (classical music) closer to
                what I would hear in an auditorium that that which one normally gets
                with a home stereo setup.

                Regards

                Jose
              • Robert Greene
                It is absolutely true that Ralph G is aiming for more truthful reproduction. But I think this will really work only if one makes recordings for it. I think I
                Message 7 of 13 , Aug 3, 2008
                  It is absolutely true that Ralph G is aiming for more truthful
                  reproduction. But I think this will really work only if one makes
                  recordings for it.

                  I think I did not make myself clear here. Let me try again:

                  Stereo as it has been practiced in the past was intended to be
                  heard a certain way which is quite different from the XTC way.

                  It may be true that listening to it some alternative way makes it
                  sound "more like music" whatever that might mean. But it surely will
                  not make it sound more like what the people that made the recordings
                  anticipated they would sound like.

                  There are really two different ways of thinking here:

                  One is that most recordings were more or less random, by guess and
                  by golly, not even monitored in any reasonable way and generally are
                  just raw material from which one tries to manufacture some sort of
                  thing that sounds like music by doing whatever is necessary on
                  playback.

                  The second view is that the masters and mistresses of recording in
                  the past had a very precise idea of what they were doing, monitored
                  very carefully, and adjusted things to be just so for the kind of
                  playback they anticipated, and that consequently one ought to play
                  things back the way that was anticipated so that one heard this
                  rather precisely intended sound.

                  The things one should do for playback is quite different depending on
                  which view one takes.

                  Perhaps the truth lies in between. And of course it depends on
                  which recordings you are listening to.

                  We have talked about this often.

                  The main point I was trying to get at was this:

                  Stereo was recorded with the idea that the crosstalk would exist.
                  If you cancel it, recordings are altered to be something other than
                  what was anticipated. This has nothing to do with whether they sound
                  more or less like music. If they change, they change. You are no
                  longer hearing what the people who monitored the recordings heard.
                  Maybe this does not matter to you. But it is true.

                  One thing that did and does make sense to me is the use of a small
                  barrier to block higher frequency crosstalk. Since the top end
                  crosstalk(the partial failure of the high frequency head shadowing
                  effect) has no positive result in any theory of stereo and is just
                  an inevitable artifact, getting rid of it seems reasonable. But it
                  is precisely in the top end that one cannot do this with electronic
                  means (except for a clamped heaed listener). It is ironic that the
                  thing you really want to do requires not electronics, but just a
                  pillow or a piece of foam. And of course it is free.

                  But also of course, capitalism being as it is, you are unlikely to
                  read this in anyone's ads.

                  People are also trying to persuade you to get bent out of shape
                  about the errors of adding two mono signals to get a single centered
                  signal. These errors do exist. I have been mentioning this off and
                  on for many years(eg a column in issue 99 as I recall reprinted here

                  http://www.regonaudio.com/Mono.html

                  along with various other aspects of stereo having to do with adding
                  things together.

                  These are not new issues, not to me, not to anyone who has been
                  around audio and thought about it seriously. Most of the issues were
                  mentioned by Blumlein in his writings in the 1930s!

                  On the other hand, I would take it for fairly obvious that these
                  issues have not really weighed too heavily upon people.

                  If they disturb you, I would suggest experimenting with Trifield,
                  which uses a center channel. It does not require a semiclamped head
                  and involve phase-y stuff. The physical barrier thing is also rather
                  pleasing and so easy--just pick up a thin pillow and hold it in
                  front of you, touching your nose and pointing out straight ahead.

                  Personally, I have never found the phase-y systems very satisfying
                  in the long run--so far. There is an immediate "golly gee" feeling,
                  partly I think because there is so much contradiction of the
                  acoustics of the listening room that one feels transported.
                  But the effect wears. There have been many, Transaural(trademark),
                  Sonic Hologram(TM), Q Sound(TM), AVS stereo(Finsterle's system).
                  All have faded from sight. In the end, I think they get on people
                  nerves--except maybe Finsterle's thing, which never got a proper
                  chance in the market place.

                  Meanwhile, the small physical barrier thing is lying free on your
                  sofa.

                  Incidentally, the way I generate surround from stereo is
                  considerably less of a sound effect in my opinion than is
                  something like the stereo dipole. It is a logical way to extract and
                  present information actually present in the recording which does not
                  give any sense of phaseiness nor alteration of the direct sound at
                  all. It does not change the direct sound in any way.

                  REG





                  --- In regsaudioforum@yahoogroups.com, "Jose Ramos" <jramos@...>
                  wrote:
                  >
                  > Hi Robert
                  >
                  > --- In regsaudioforum@yahoogroups.com, "Robert Greene"
                  > <regonaudio@> wrote:
                  > > But it seems to me that it is important to realize that ,however
                  > > much fun these things are--and of course there will be more and
                  > more
                  > > of them since digital processing with computers is effectively
                  free-
                  > -
                  > > this has rather little to do with reproducing recordings as they
                  > > were made to be heard.
                  >
                  > With respect, are you perhaps not missing the point about systems
                  > such as Ambiophonics? The developers of these systems would argue
                  > that their whole aim is to in fact recreate the original sound of
                  the
                  > recording by eliminating the problems of playback in a stereo
                  system
                  > in the home environment. This is different to playing around with
                  > the sound to create effects, however pleasing, that are not true
                  to
                  > the original. Examples of the latter would include DSP hall-
                  effects,
                  > multichannel from stereo etc.
                  >
                  > I am a long-time Tact RCS user and have listened to the XTC
                  function
                  > which I do not particularly like in that it does not recreate a
                  sense
                  > of the original recording IMO - BUT I have not used it correctly
                  as I
                  > have not set up my speakers close together as is required. I thus
                  > reserve any judgement about the efficacy of XTC to recreate the
                  > original sound and defer to the findings of others such as Tom who
                  > has actually implemented it properly.
                  > I have heard the XTC properly set up at the 2007 NY HES and at
                  Ralph
                  > Glasgals home - in these setups, I was impressed by what XTC could
                  do
                  > and did feel that I was hearing sound (classical music) closer to
                  > what I would hear in an auditorium that that which one normally
                  gets
                  > with a home stereo setup.
                  >
                  > Regards
                  >
                  > Jose
                  >
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