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Re: [linuxham] fldigi makes Macbook fan run full time

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  • Brian Lloyd
    ... And if I didn t have to do sample-rate conversion, I wouldn t have to use the interpolator at all. What is the internal sample rate that you use in the
    Message 1 of 20 , Aug 2, 2009
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      On Sun, Aug 2, 2009 at 1:07 PM, w1hkj<w1hkj@...> wrote:
      > You might be able to reduce cpu usage by judicious selection of the sound
      > card interpolator.  The "Fast Interpolator" might provide more than adequate
      > sample rate conversion at a much reduced cpu load.

      And if I didn't have to do sample-rate conversion, I wouldn't have to
      use the interpolator at all. What is the internal sample rate that you
      use in the software? I know that when I am using PowerSDR I can
      specifiy the sample rate on the audio channel going to/from fldigi. If
      I use the native rate used by fldigi then fldigi won't have to do any
      rate conversion. PowerSDR will already have done that. (In fact, I
      suspect that both PowerSDR and fldigi are already doing sample rate
      conversion on the same stream.) By default PowerSDR uses a sample rate
      of 48KHz but I believe it can generate any of the standards that are
      integer divisors of 44.1KHz and 48KHz, e.g. 8KHz, 11.025KHz, 12KHz,
      22.05KHz, 24KHz, etc.

      --
      73 de Brian, WB6RQN/J79BPL
    • w1hkj
      ... 8000 and 11025 depending on mode. refer to the source code for each individual encoder / decoder. Dave
      Message 2 of 20 , Aug 2, 2009
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        Brian Lloyd wrote:
        On Sun, Aug 2, 2009 at 1:07 PM, w1hkj<w1hkj@...> wrote:
          
        You might be able to reduce cpu usage by judicious selection of the sound
        card interpolator.  The "Fast Interpolator" might provide more than adequate
        sample rate conversion at a much reduced cpu load.
            
        And if I didn't have to do sample-rate conversion, I wouldn't have to
        use the interpolator at all. What is the internal sample rate that you
        use in the software? I know that when I am using PowerSDR I can
        specifiy the sample rate on the audio channel going to/from fldigi. If
        I use the native rate used by fldigi then fldigi won't have to do any
        rate conversion. PowerSDR will already have done that. (In fact, I
        suspect that both PowerSDR and fldigi are already doing sample rate
        conversion on the same stream.) By default PowerSDR uses a sample rate
        of 48KHz but I believe it can generate any of the standards that are
        integer divisors of 44.1KHz and 48KHz, e.g. 8KHz, 11.025KHz, 12KHz,
        22.05KHz, 24KHz, etc.
        
          
        8000 and 11025 depending on mode.  refer to the source code for each individual encoder / decoder.

        Dave
      • Brian Lloyd
        ... Hmm, then clearly it makes no sense to send the bit stream at 48KHz. Why the difference? It seems to me that it would be simpler to make all the codecs run
        Message 3 of 20 , Aug 2, 2009
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          On Sun, Aug 2, 2009 at 2:11 PM, w1hkj<w1hkj@...> wrote:

          > 8000 and 11025 depending on mode.  refer to the source code for each
          > individual encoder / decoder.

          Hmm, then clearly it makes no sense to send the bit stream at 48KHz.
          Why the difference? It seems to me that it would be simpler to make
          all the codecs run at the same sample rate.

          Is the code smart enough to know when sample-rate conversion is not
          needed, i.e. that the actual sample rate and the desired sample rate
          are the same?

          --
          73 de Brian, WB6RQN/J79BPL
        • Stelios Bounanos
          ... You can set the capture & playback sample rates to Auto , and then fldigi will always try to open the audio device at the modem s sample rate (8000 or
          Message 4 of 20 , Aug 2, 2009
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            >>>>> On Sun, 2 Aug 2009 14:04:30 -0700, Brian Lloyd <brian-wb6rqn@...> said:

            > On Sun, Aug 2, 2009 at 1:07 PM, w1hkj<w1hkj@...> wrote:
            >> You might be able to reduce cpu usage by judicious selection of the sound
            >> card interpolator.  The "Fast Interpolator" might provide more than adequate
            >> sample rate conversion at a much reduced cpu load.

            > And if I didn't have to do sample-rate conversion, I wouldn't have to
            > use the interpolator at all.

            You can set the capture & playback sample rates to "Auto", and then
            fldigi will always try to open the audio device at the modem's sample
            rate (8000 or 11025 Hz). Of course, if your audio device does not
            support these rates there will still be resampling, but this time it
            will be done by CoreAudio. On OS X, IIRC, PortAudio sets things up so
            that any such resampling is done at the maximum available quality,
            probably equivalent to libsamplerate's Medium or Best Sinc.

            BTW there is an interesting resampler comparison here:

            http://src.infinitewave.ca/


            --

            73,
            Stelios, M0GLD.
          • Stelios Bounanos
            ... This is what the Auto sample rate does, with a fall-back to Native if the modem s rate is not supported by the sound card. Auto used to be the default
            Message 5 of 20 , Aug 2, 2009
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              >>>>> On Sun, 2 Aug 2009 14:20:25 -0700, Brian Lloyd <brian-wb6rqn@...> said:

              > On Sun, Aug 2, 2009 at 2:11 PM, w1hkj<w1hkj@...> wrote:
              >> 8000 and 11025 depending on mode.  refer to the source code for each
              >> individual encoder / decoder.

              > Hmm, then clearly it makes no sense to send the bit stream at 48KHz.
              > Why the difference? It seems to me that it would be simpler to make
              > all the codecs run at the same sample rate.

              > Is the code smart enough to know when sample-rate conversion is not
              > needed, i.e. that the actual sample rate and the desired sample rate
              > are the same?

              This is what the "Auto" sample rate does, with a fall-back to "Native"
              if the modem's rate is not supported by the sound card. Auto used to be
              the default option but we had to change it to Native because some
              systems claim to support every standard sample rate... using really
              crappy linear interpolation.


              --

              73,
              Stelios, M0GLD.
            • Brian Lloyd
              ... -- 73 de Brian, WB6RQN/J79BPL
              Message 6 of 20 , Aug 2, 2009
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                On Sun, Aug 2, 2009 at 2:36 PM, Stelios Bounanos<lham@...> wrote:
                >
                >
                >>>>>> On Sun, 2 Aug 2009 14:20:25 -0700, Brian Lloyd
                >>>>>> <brian-wb6rqn@...> said:
                >
                >> On Sun, Aug 2, 2009 at 2:11 PM, w1hkj<w1hkj@...> wrote:
                >>> 8000 and 11025 depending on mode.  refer to the source code for each
                >>> individual encoder / decoder.
                >
                >> Hmm, then clearly it makes no sense to send the bit stream at 48KHz.
                >> Why the difference? It seems to me that it would be simpler to make
                >> all the codecs run at the same sample rate.
                >
                >> Is the code smart enough to know when sample-rate conversion is not
                >> needed, i.e. that the actual sample rate and the desired sample rate
                >> are the same?
                >
                > This is what the "Auto" sample rate does, with a fall-back to "Native"
                > if the modem's rate is not supported by the sound card. Auto used to be
                > the default option but we had to change it to Native because some
                > systems claim to support every standard sample rate... using really
                > crappy linear interpolation.
                >
                > --
                >
                > 73,
                > Stelios, M0GLD.
                >
                >



                --
                73 de Brian, WB6RQN/J79BPL
              • Brian Lloyd
                ... Sounds like the goal is really to make sure fldigi doesn t have to resample. -- 73 de Brian, WB6RQN/J79BPL
                Message 7 of 20 , Aug 2, 2009
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                  On Sun, Aug 2, 2009 at 2:36 PM, Stelios Bounanos<lham@...> wrote:
                  >> Is the code smart enough to know when sample-rate conversion is not
                  >> needed, i.e. that the actual sample rate and the desired sample rate
                  >> are the same?
                  >
                  > This is what the "Auto" sample rate does, with a fall-back to "Native"
                  > if the modem's rate is not supported by the sound card. Auto used to be
                  > the default option but we had to change it to Native because some
                  > systems claim to support every standard sample rate... using really
                  > crappy linear interpolation.

                  Sounds like the goal is really to make sure fldigi doesn't have to resample.

                  --
                  73 de Brian, WB6RQN/J79BPL
                • Brian Lloyd
                  ... Well the goal is to avoid resampling in fldigi. That implies to me that I need to make the source match fldigi rather than the other way around. I could go
                  Message 8 of 20 , Aug 2, 2009
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                    On Sun, Aug 2, 2009 at 2:32 PM, Stelios Bounanos<lham@...> wrote:
                    >> And if I didn't have to do sample-rate conversion, I wouldn't have to
                    >> use the interpolator at all.
                    >
                    > You can set the capture & playback sample rates to "Auto", and then
                    > fldigi will always try to open the audio device at the modem's sample
                    > rate (8000 or 11025 Hz). Of course, if your audio device does not
                    > support these rates there will still be resampling, but this time it
                    > will be done by CoreAudio.

                    Well the goal is to avoid resampling in fldigi. That implies to me
                    that I need to make the source match fldigi rather than the other way
                    around.

                    I could go dig through the source code for fldigi to find the native
                    sample rates for the various modems. But given that I have never
                    looked at the source code, it would probably take awhile to figure out
                    where to look. I don't like asking people to do things for me but
                    given as you or Dave could probably tell me off the top of your heads
                    where to look (or cut an paste the relevant section of the constant
                    declarations) I am going to ask.

                    > On OS X, IIRC, PortAudio sets things up so
                    > that any such resampling is done at the maximum available quality,
                    > probably equivalent to libsamplerate's Medium or Best Sinc.
                    >
                    > BTW there is an interesting resampler comparison here:
                    >
                    > http://src.infinitewave.ca/

                    Interesting, to say the least. All resamplers are not created equal,
                    eh? I was heartened to see that the resampler in Apple's Coreaudio is
                    pretty darned good. How is resampling done in auto on Windows systems?


                    --
                    73 de Brian, WB6RQN/J79BPL
                  • w1hkj
                    ... As Stelios pointed out in a separate response that really is not necessary Brian. Use the auto and if your sound driver supports the request the modem
                    Message 9 of 20 , Aug 2, 2009
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                      Brian Lloyd wrote:
                      On Sun, Aug 2, 2009 at 2:32 PM, Stelios Bounanos<lham@...> wrote:
                        
                      And if I didn't have to do sample-rate conversion, I wouldn't have to
                      use the interpolator at all.
                            
                      You can set the capture & playback sample rates to "Auto", and then
                      fldigi will always try to open the audio device at the modem's sample
                      rate (8000 or 11025 Hz). Of course, if your audio device does not
                      support these rates there will still be resampling, but this time it
                      will be done by CoreAudio.
                          
                      Well the goal is to avoid resampling in fldigi. That implies to me
                      that I need to make the source match fldigi rather than the other way
                      around.
                      
                      I could go dig through the source code for fldigi to find the native
                      sample rates for the various modems. But given that I have never
                      looked at the source code, it would probably take awhile to figure out
                      where to look. I don't like asking people to do things for me but
                      given as you or Dave could probably tell me off the top of your heads
                      where to look (or cut an paste the relevant section of the constant
                      declarations) I am going to ask.
                        
                      As Stelios pointed out in a separate response that really is not necessary Brian.  Use the "auto" and if your sound driver supports the request the modem native sample rate will be used.

                      For those systems that do not support such a response and lie about their capability (mostly MS systems) the resampling code in fldigi is far superior to what most outboard drivers provide.  It is then much better to operate the sound system in its sound card clock native mode.  That might be 44100, 48000, 96000, whatever.  The resamplers in fldigi are from the SecretRabbit site.  Take a look at the specs available on that web site.  Several types of resampling are provided so that fldigi can continue (even if degraded) on cpu starved systems.  fldigi measures you system performance on the initial start and selects the optimum resampler based on that measurement.

                      These are the sample rates you requested:

                      PSK (all baud rates)
                      8000
                      MFSK 4 / 8 / 16 / 31 / 32 / 64
                      8000
                      MFSK 11 / 22
                      11025
                      DOMINOEX 5 / 11 / 22
                      11025
                      DOMINOEX 4 / 8 / 16
                      8000
                      THOR 5 / 11 / 22
                      11025
                      DOMINOEX 4 / 8 / 16
                      8000
                      FELD
                      8000
                      MT63
                      8000
                      OLIVIA
                      8000
                      THROB
                      8000



                      Dave
                    • Brian Lloyd
                      ... I guess I wasn t being clear. I am running PowerSDR, the processing behind the Flex 5000. There is no sound card. The digital baseband stream (or low IF if
                      Message 10 of 20 , Aug 2, 2009
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                        On Sun, Aug 2, 2009 at 6:02 PM, w1hkj<w1hkj@...> wrote:
                        > For those systems that do not support such a response and lie about their
                        > capability (mostly MS systems) the resampling code in fldigi is far superior
                        > to what most outboard drivers provide.  It is then much better to operate
                        > the sound system in its sound card clock native mode.  That might be 44100,
                        > 48000, 96000, whatever.

                        I guess I wasn't being clear. I am running PowerSDR, the processing
                        behind the Flex 5000. There is no sound card. The digital baseband
                        stream (or low IF if you prefer) is being fed to fldigi from PowerSDR
                        through VAC (Virtual Audio Cable). The "radio" (PowerSDR) provides a
                        digital stream. There is no A:D or D:A involved between PowerSDR and
                        fldigi. Also, PowerSDR has no "native" sample rate. PowerSDR is using
                        48KHz, 96KHz, or 192KHz depending on the sample rate I select for the
                        ADC in the front-end. PowerSDR then allows me to specify the sample
                        rate to send to the digital mode program via VAC. Therefore the
                        resampling takes place in PowerSDR. (And you have me wondering just
                        how good it is.)

                        Since I normally run the radio at 96KHz PowerSDR is going to resample
                        for me no matter what because 48KHz (the default value) is the highest
                        sample rate that VAC supports. Since I must resample anyway, by
                        telling PowerSDR to resample down to 8KHz or 11.025KHz I avoid the
                        need to have fldigi resample a second time.

                        > The resamplers in fldigi are from the SecretRabbit
                        > site.  Take a look at the specs available on that web site.  Several types
                        > of resampling are provided so that fldigi can continue (even if degraded) on
                        > cpu starved systems.  fldigi measures you system performance on the initial
                        > start and selects the optimum resampler based on that measurement.

                        I understand but since PowerSDR is resampling for me anyway (and
                        generating whatever artifacts it is going to generate :-) it seems to
                        me that resampling a second time in fldigi is not going to improve
                        things.

                        > These are the sample rates you requested:

                        Thank you. Perfect. I am going to experiment with having PowerSDR
                        resample down to either 8KHz or 11.025KHz to see if it improves
                        performance any. I will also see if it reduces CPU utilization.

                        Too bad there is no communication between the two programs as it seems
                        to me that the best solution is for them to cooperate to resample only
                        once and then to have the CODECs communicate the optimum sample rate
                        back to the source, i.e. PowerSDR. In the mean time, I can do it
                        manually. Knowing the native sample rates for the CODECs will let me
                        select the correct one at PowerSDR so that fldigi doesn't need to
                        resample.

                        >
                        > PSK (all baud rates)
                        > 8000
                        > MFSK 4 / 8 / 16 / 31 / 32 / 64
                        > 8000
                        > MFSK 11 / 22
                        > 11025
                        > DOMINOEX 5 / 11 / 22
                        > 11025
                        > DOMINOEX 4 / 8 / 16
                        > 8000
                        > THOR 5 / 11 / 22
                        > 11025
                        > DOMINOEX 4 / 8 / 16
                        > 8000
                        > FELD
                        > 8000
                        > MT63
                        > 8000
                        > OLIVIA
                        > 8000
                        > THROB
                        > 8000

                        --
                        73 de Brian, WB6RQN/J79BPL
                      • w1hkj
                        ... I would be very interested in learning the results of your tests Brian. Dave
                        Message 11 of 20 , Aug 3, 2009
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                          Brian Lloyd wrote:
                          >
                          > Thank you. Perfect. I am going to experiment with having PowerSDR
                          > resample down to either 8KHz or 11.025KHz to see if it improves
                          > performance any. I will also see if it reduces CPU utilization.

                          I would be very interested in learning the results of your tests Brian.

                          Dave
                        • Brian Lloyd
                          ... Certainly. You are doing much more work on this than I. Anything I can do to make your work more effective I will. -- 73 de Brian, WB6RQN/J79BPL
                          Message 12 of 20 , Aug 3, 2009
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                            On Mon, Aug 3, 2009 at 3:19 AM, w1hkj<w1hkj@...> wrote:
                            >
                            >
                            > Brian Lloyd wrote:
                            >>
                            >> Thank you. Perfect. I am going to experiment with having PowerSDR
                            >> resample down to either 8KHz or 11.025KHz to see if it improves
                            >> performance any. I will also see if it reduces CPU utilization.
                            >
                            > I would be very interested in learning the results of your tests Brian.

                            Certainly. You are doing much more work on this than I. Anything I can
                            do to make your work more effective I will.

                            --
                            73 de Brian, WB6RQN/J79BPL
                          • Dick Kriss
                            After reading the recent comments on sampling rates, I recalled a note from Dec 2008 where Chen W7AY changed the default sampling rate setting for his
                            Message 13 of 20 , Aug 3, 2009
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                              After reading the recent comments on sampling rates, I
                              recalled a note from Dec 2008 where Chen W7AY changed
                              the default sampling rate setting for his cocoaModem to
                              16000 samples per second due to some technical issues
                              between the Burr-Brown PCM2902 codec chipset and the
                              Mac OS X Core Audio.

                              The Burr-Brown chipset is used in sound cards such as as the
                              microHAM digiKeyer, the Edirol UA-1X and the SignaLink USB.

                              The topic is discussed in W7AY's "What has changed in v0.62" at

                              <http://homepage.mac.com/chen/w7ay/cocoaModem/Whats%20New/index.html>

                              The bottom line was W7AY recommend users avoid using 11025
                              and 44100 samples per sec and he changed the default Rx in his
                              cocoaModem to 16000 samples per sec.

                              At the time I really did not understand the technical issue but
                              changing to his recommend 16000 samples per second for Rx
                              helped cocoaModem decoding.

                              When I changed from cocoaModem to fldigi, I set the
                              Sound Card/Audio/Settings to Capture at 16000 samples/sec
                              (vs. the native 32000) and I left Playback at the native 32000
                              samples/sec. I did not understand the "Converter" so set it
                              to Medium.

                              To see what would happen I just changed my fldigi Capture
                              setting back to the native 32000 samples per second and
                              fldigi seems to work fine. Maybe Apple has changed the OS X
                              Core Audio since W7AY's note that was posted in Dec 2008.

                              I wonder what Capture/Converter settings other fldigi Mac OS X
                              and SignaLink US/users are using?

                              73 Dick AA5VU
                            • ke7adu
                              OK, I have been playing around with the Sample Rate and Converter settings. My install was set to Native I set to Auto did not notice any change in CPU use.
                              Message 14 of 20 , Aug 3, 2009
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                                OK,

                                I have been playing around with the Sample Rate and Converter settings. My install was set to Native I set to Auto did not notice any change in CPU use. Changing the Converter settings from Medium Sync to Linear drops CPU use by a few percent.

                                CocoaModem runs about 6% CPU use while fldigi runs between 16% and 25% CPU. However, the Cocoa Modem table view is only decoding two to three signals while fldigi is decoding six to eight signals in the PSK Browser so I can see why it would use more CPU.

                                Anthony - KE7ADU

                                --- In linuxham@yahoogroups.com, "ke7adu" <ke7adu@...> wrote:
                                >
                                > First let me say that I am really enjoying using fldidi on my Macbook. Good HAM software for OS X is hard to find (especially for free). Second I am new to the Mac OS but I have been using Windows and playing with Linux for years.
                                >
                                > Now down to business.
                                >
                                > When fldigi is loaded the fan on my Macbook runs continuously. Normally it never runs. That is not a big deal except I figure that will lead to a short battery life if I decide to operate in the field.
                                > CocoaModem doesn't seem to make the fan run but for what I do I prefer fldigi.
                                >
                                > I plan to try fldidg on a Windows and Linux box and see if I have the same issue.
                                >
                                > Anyone else with this issue? Anyone have suggestions as to how to temper the CPU use when I am operating off battery?
                                >
                                > My equipment:
                                > Computer: Macbook Aluminum 2.0 GHz, 4 GB RAM
                                > Interface: SignaLink USB
                                > OS X ver: 10.5.7
                                > Radio: FT-897D
                                >
                                > Thanks,
                                > Anthony - KE7AUD
                                >
                              • w1hkj
                                ... BINGO ! If you were decoding 20 the cpu usage might be more yet. cpu usage will also be a function of the modem and baud rate that is being used. Don t
                                Message 15 of 20 , Aug 3, 2009
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                                  ke7adu wrote:
                                  > OK,
                                  >
                                  > I have been playing around with the Sample Rate and Converter settings. My install was set to Native I set to Auto did not notice any change in CPU use. Changing the Converter settings from Medium Sync to Linear drops CPU use by a few percent.
                                  >
                                  > CocoaModem runs about 6% CPU use while fldigi runs between 16% and 25% CPU. However, the Cocoa Modem table view is only decoding two to three signals while fldigi is decoding six to eight signals in the PSK Browser so I can see why it would use more CPU.
                                  >
                                  BINGO ! If you were decoding 20 the cpu usage might be more yet. cpu
                                  usage will also be a function of the modem and baud rate that is being used.

                                  Don't recommend Linear ... your OS X box should be more that fast enough
                                  to support the Medium or Fast Sync converter.

                                  Dave
                                • Brian Lloyd
                                  ... I ran some tests last night, qualitative rather than quantitative, i.e. the results were subjective rather than objective -- no measurements. Before I get
                                  Message 16 of 20 , Aug 4, 2009
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                                    On Mon, Aug 3, 2009 at 3:19 AM, w1hkj<w1hkj@...> wrote:
                                    >
                                    >
                                    > Brian Lloyd wrote:
                                    >>
                                    >> Thank you. Perfect. I am going to experiment with having PowerSDR
                                    >> resample down to either 8KHz or 11.025KHz to see if it improves
                                    >> performance any. I will also see if it reduces CPU utilization.
                                    >
                                    > I would be very interested in learning the results of your tests Brian.

                                    I ran some tests last night, qualitative rather than quantitative,
                                    i.e. the results were subjective rather than objective -- no
                                    measurements. Before I get into it I thought I would explain my setup
                                    just so everyone understands why what I am doing is a bit different.

                                    I am running a Flex 5000a software-defined radio. Unlike most
                                    digital-mode setups there is no sound-card involved since the radio
                                    software provides data to fldigi in digital form. No analog to digital
                                    or digital to analog conversion before fldigi. Most rigs have the
                                    following signal processing chain:

                                    antenna>1st mixer>roofing filter>2nd
                                    mixer>A:D>DSP>D:A>cables>A:D(soundcard)>fldigi

                                    In my setup I have the following signal processing chain:

                                    antenna>1st mixer>A:D>DSP>fldigi

                                    As you can see it is much simpler and once the signal has been
                                    converted from analog to digital right after the mixer it is never
                                    converted back to analog. It is pure digital all the way through to
                                    the digital mode program. (Note, this works for any digital mode
                                    program including DM780, not just fldigi.) The potential is for much
                                    higher quality since intermediate conversions have been eliminated.
                                    Performance is not dependent on eliminating ground loops, eliminating
                                    RF pick-up, sound-card quality/sample rate/bit depth, etc.

                                    The "DSP" software really is the radio. It is called PowerSDR and
                                    implements all the functions for the Flex 5000. There are no controls
                                    on the radio hardware itself. Everything is handled by the software.
                                    The analog-to-digital conversion takes place in the RF hardware using
                                    a very high performance A:D converter with a bit-depth of 24 bits and
                                    a sample rate of 48KHz, 96KHz, or 192KHz. (I normally run at 96KHz.)
                                    Once the radio hardware has performed this conversion the signal is
                                    never converted back into analog form. It remains in digital form all
                                    the way through to the digital mode program. (I normally run fldigi or
                                    DM780.)

                                    (The only difference to this is the case of audio modes, e.g. CW or
                                    SSB where the signal is converted back to analog in order to drive the
                                    speaker and/or headphones.)

                                    As you recall from a couple of days ago, I was asking about native
                                    sample rates for the CODECs (COders/DECoders). The reason is, it
                                    seemed to me that it would be a waste to do sample rate conversion
                                    twice, once in PowerSDR and a second time in fldigi. By default
                                    PowerSDR provides its digital "audio" (I prefer the term "baseband" or
                                    "low IF" because it is not the final output signal -- that is the text
                                    on the screen) signal at a sample rate of 48000 Hz. Fldigi then does a
                                    second sample rate conversion to either 8000 Hz or 11025 Hz depending
                                    on the CODEC chosen by the operator. Since PowerSDR is already doing
                                    the sample rate conversion from 96 KHz to 48 KHz it seemed a waste to
                                    me to then have fldigi go through the sample rate conversion process
                                    yet again. It seemed better to just let PowerSDR do the sample rate
                                    conversion directly to 8000 Hz or 11025 Hz and eliminate a step.

                                    I spent some time last night monitoring PSK31 and Olivia signals
                                    letting PowerSDR perform the sample rate conversion to 8000 Hz.
                                    Subjectively I could discern no obvious improvement or degradation
                                    over the double-rate-conversion that was going on previously. What I
                                    did notice is that the waterfall was showing substantial aliasing
                                    products in the passband. It appears that PowerSDR is *NOT* doing
                                    sufficient anti-aliasing at the lower sample rate. Given that the Flex
                                    5000 can produce substantial power 48KHz from the LO injection
                                    frequency (at a 96KHz sample rate) it stands to reason that there
                                    needs to be a brick wall filter for all power above the Nyquist
                                    frequency at the intermediate rate of the CODEC, i.e. one half the
                                    sample rate or 4 KHz in the case of 8 KHz sampling. This does not
                                    appear to be the case.

                                    So, until the downsampling in PowerSDR gets improved anti-aliasing
                                    filtering, it seems to me that it is better to continue sending a 48
                                    KHz data stream to fldigi and allow fldigi to do the downsampling to
                                    the 8000 Hz or 11025 Hz sample rate expected by the CODECs.

                                    I guess I need to go bug the guys over at Flex now. ;-)

                                    --
                                    73 de Brian, WB6RQN/J79BPL
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