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Re: [cosmacelf] Re: Cassette to MP3 Converter

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  • Ray Sills
    True, MP3 is lossy. But, that may not matter when you are trying to record or reproduce two tones that are frequency shift keyed to designate encode a
    Message 1 of 13 , Jul 13 9:45 AM
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      True, MP3 is lossy. But, that may not matter when you are trying to
      record or reproduce two tones that are frequency shift keyed to
      designate encode a sequence of 1s and 0s. You certainly do not -
      need- to "compress" (data reduce) the content for a 4K binary file.
      Even using AIFF or WAV files won't create very large files, especially
      by today's standards where 4K is the smallest size file stored on a
      modern HD... at least on my iMac.

      The FSK tones usually used are well in the normal voice frequency
      (telephone quality) spectrum. And, the tape format is normally quite
      tolerant of frequency variations caused by wow and flutter or off-
      speed that might be expected in a cheap cassette machine. I know that
      the RCA VIP used frequencies of 800 Hz and 2000 Hz to differentiate
      the data 1s and 0s. The VIP tape format output 4 seconds of 2000 Hz
      tone as a header to synchronize the tape read routines, followed by
      2.5 seconds of varying tones per 256 byte block (page). Bytes always
      start with a 1 start bit, followed by 8 data bits, and end with a
      parity bit.. (odd parity).

      So, my take on it is that while MP3 offers no huge advantage, it
      should be OK for saving and loading data. That said, I have not tried
      it, and it would be an interesting experiment to see how it might work
      or not work.

      73 de Ray



      On Jul 11, 2013, at 3:38 PM, somaspack wrote:

      > MP3 is lossy, maybe ok for music but bad for must-have bits.
      >
      > Scott
    • bill rowe
      My original thought was that this thing probably depended on pc software for the mp3 conversion and you could maybe get it to save a wav file instead for input
      Message 2 of 13 , Jul 13 10:54 AM
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        My original thought was that this thing probably depended on pc software for the mp3 conversion and you could maybe get it to save a wav file instead for input to richard's conversion tool.

        On 2013-07-13, at 12:45 PM, "Ray Sills" <raysills3@...> wrote:

         

        True, MP3 is lossy. But, that may not matter when you are trying to
        record or reproduce two tones that are frequency shift keyed to
        designate encode a sequence of 1s and 0s. You certainly do not -
        need- to "compress" (data reduce) the content for a 4K binary file.
        Even using AIFF or WAV files won't create very large files, especially
        by today's standards where 4K is the smallest size file stored on a
        modern HD... at least on my iMac.

        The FSK tones usually used are well in the normal voice frequency
        (telephone quality) spectrum. And, the tape format is normally quite
        tolerant of frequency variations caused by wow and flutter or off-
        speed that might be expected in a cheap cassette machine. I know that
        the RCA VIP used frequencies of 800 Hz and 2000 Hz to differentiate
        the data 1s and 0s. The VIP tape format output 4 seconds of 2000 Hz
        tone as a header to synchronize the tape read routines, followed by
        2.5 seconds of varying tones per 256 byte block (page). Bytes always
        start with a 1 start bit, followed by 8 data bits, and end with a
        parity bit.. (odd parity).

        So, my take on it is that while MP3 offers no huge advantage, it
        should be OK for saving and loading data. That said, I have not tried
        it, and it would be an interesting experiment to see how it might work
        or not work.

        73 de Ray

        On Jul 11, 2013, at 3:38 PM, somaspack wrote:

        > MP3 is lossy, maybe ok for music but bad for must-have bits.
        >
        > Scott

      • joshbensadon
        ... Hi Ray, I feel the same way, but, like you, I have not experimented with it so I don t know for sure. I agree with your basic argument which is these
        Message 3 of 13 , Jul 13 1:17 PM
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          --- In cosmacelf@yahoogroups.com, Ray Sills <raysills3@...> wrote:
          >
          > So, my take on it is that while MP3 offers no huge advantage, it
          > should be OK for saving and loading data. That said, I have not tried
          > it, and it would be an interesting experiment to see how it might work
          > or not work.

          Hi Ray,

          I feel the same way, but, like you, I have not experimented with it so I don't know for sure. I agree with your basic argument which is these compilations are nothing more than ONE signal of two alternating tones. I can't see how MP3 can mess that up. Now here comes the big "BUT". The human ear is very forgiving, in fact, I'm sure we can still hear a song playing even after you turn off the audio (or are those just the voices in my head?). My point is, perhaps MP3 at some point starts adding new transitions on the signal? It might be convenient to skip a phase transition just to create a pattern. That skip might not be heard by the human ear, but apparently ELF ears are much keener.

          It would definitely be a fun experiment, I will also conduct the same one here... some day. MP3 comes in different degrees of compression, so that will likely have an impact?

          Up to now, I've heard the masses on line saying it doesn't work, so I have to bow to those pioneers that have already tried it.

          :)J
        • Egan Ford
          ... The tones are not relevant, at least that is the case for the Apple II. All that is measured is the number of cycles between zero crossings. The default
          Message 4 of 13 , Jul 13 4:11 PM
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            > True, MP3 is lossy. But, that may not matter when you are trying to
            > record or reproduce two tones that are frequency shift keyed to
            > designate encode a sequence of 1s and 0s.

            The tones are not relevant, at least that is the case for the Apple
            II. All that is measured is the number of cycles between zero
            crossings. The default for the Apple II is 1000 Hz for a 0 and 2000
            Hz for a 1. It's up to the programmer to count the cycles to
            determine 0 or 1 (and there is always a + or - to consider).

            > So, my take on it is that while MP3 offers no huge advantage, it
            > should be OK for saving and loading data. That said, I have not tried
            > it, and it would be an interesting experiment to see how it might work
            > or not work.

            I've download and used MP3s that work just fine with the Apple II,
            OTOH the ones that I have created have been hit or miss (probably some
            setting). I speculate that the lossy compression may alter the
            waveform and skip some of the zero crossings. Depending on how
            tolerant the programmer was with ranges for 0 and 1 may determine if
            they work. The 1000 Hz/2000 Hz range is fairly tolerant to issues
            with different tape players, volume, tape stretch, etc... so I agree
            is might work.

            For my asciiexpress.net project I created my own audio code using 6000
            Hz/12000 Hz to up the default 1333 bps to 8000 bps (I also threw in
            compression to get 2x more on average). On some machines I can push
            the native rate to 9600 bps, but it does not work on all machines--I
            think have reached the tolerances of the HW design. MP3 for this
            higher frequency download code hasn't worked out. Between data
            compression and using higher frequency the AIFF/WAV files are smaller
            as well further reducing any advantage of MP3 size.

            I think another issue I may have encountered with MP3 was the player
            and how the player did the D2A. It's been about 2 years since I
            explored MP3 as an option, but I recall getting different results with
            different players. AIFF/WAV have universally worked. I didn't take
            very good notes, I was just trying to get results.

            Lastly, I wonder if taking an original tape with all of its analog
            glory and doing tape to MP3 may work better. I wonder if that is how
            most of the MP3s that have worked for me were created. I create my
            own files as "perfect" waveforms using a tool I wrote to convert
            binary code to audio. That audio when converted to MP3 was
            problematic. Again it could just be my tight 8000-9600 bps
            requirements. And again, poor note taking.

            Cheers,

            Egan
          • bill rowe
            asciiexpress.net is very cool. You can select any of a bunch of apple programs and stream them into the cassette port of your apple from your phone.
            Message 5 of 13 , Jul 13 5:05 PM
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              asciiexpress.net is very cool. You can select any of a bunch of apple programs and stream them into the cassette port of your apple from your phone.


              On 2013-07-13, at 7:12 PM, "Egan Ford" <datajerk@...> wrote:

               

              > True, MP3 is lossy. But, that may not matter when you are trying to
              > record or reproduce two tones that are frequency shift keyed to
              > designate encode a sequence of 1s and 0s.

              The tones are not relevant, at least that is the case for the Apple
              II. All that is measured is the number of cycles between zero
              crossings. The default for the Apple II is 1000 Hz for a 0 and 2000
              Hz for a 1. It's up to the programmer to count the cycles to
              determine 0 or 1 (and there is always a + or - to consider).

              > So, my take on it is that while MP3 offers no huge advantage, it
              > should be OK for saving and loading data. That said, I have not tried
              > it, and it would be an interesting experiment to see how it might work
              > or not work.

              I've download and used MP3s that work just fine with the Apple II,
              OTOH the ones that I have created have been hit or miss (probably some
              setting). I speculate that the lossy compression may alter the
              waveform and skip some of the zero crossings. Depending on how
              tolerant the programmer was with ranges for 0 and 1 may determine if
              they work. The 1000 Hz/2000 Hz range is fairly tolerant to issues
              with different tape players, volume, tape stretch, etc... so I agree
              is might work.

              For my asciiexpress.net project I created my own audio code using 6000
              Hz/12000 Hz to up the default 1333 bps to 8000 bps (I also threw in
              compression to get 2x more on average). On some machines I can push
              the native rate to 9600 bps, but it does not work on all machines--I
              think have reached the tolerances of the HW design. MP3 for this
              higher frequency download code hasn't worked out. Between data
              compression and using higher frequency the AIFF/WAV files are smaller
              as well further reducing any advantage of MP3 size.

              I think another issue I may have encountered with MP3 was the player
              and how the player did the D2A. It's been about 2 years since I
              explored MP3 as an option, but I recall getting different results with
              different players. AIFF/WAV have universally worked. I didn't take
              very good notes, I was just trying to get results.

              Lastly, I wonder if taking an original tape with all of its analog
              glory and doing tape to MP3 may work better. I wonder if that is how
              most of the MP3s that have worked for me were created. I create my
              own files as "perfect" waveforms using a tool I wrote to convert
              binary code to audio. That audio when converted to MP3 was
              problematic. Again it could just be my tight 8000-9600 bps
              requirements. And again, poor note taking.

              Cheers,

              Egan

            • jdripper
              ... And _Beneath Apple DOS_ is flat-out wrong when they claim that there are clock bits between the bits of the nibble. The whole point of using GCR is that
              Message 6 of 13 , Jul 15 11:27 AM
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                --- In cosmacelf@yahoogroups.com, "joshbensadon" <joshbensadon@...> wrote:
                > I've already read "Beneath Apple DOS". Very good book on the floppy disk software, but falls a little short in the ordering of the 5/3 nibbilizer.

                And _Beneath Apple DOS_ is flat-out wrong when they claim that there are clock bits between the bits of the nibble. The whole point of using GCR is that it is self-clocking, so it doesn't need to throw away half the bandwidth on clock bits the way that normal single-density (FM) encoding does. That's why Apple gets 13 or 16 256-byte sectors per track where competing systems using single density only got 10 256-byte sectors.

                The 4+4 nibblization of the address mark contents is FM, a degenerate case of GCR.

                Normal double-density (MFM) encoding is even more efficient that Apple's GCR, for a given channel bandwidth, but requires more hardware than the Apple design, and more precise discrimination of the time between flux changes. To be any good, MFM requires a phase-locked-loop for recovery. The state machine of the Apple floppy controller includes a crude state machine, but not good enough for reliable MFM.

                For many years, hard drives usually used (1,7) or (2,7) RLL, which is a form of GCR that is even more efficient than MFM, but requires an even better data separator. Now most hard drives use even more complex coding than that.

                Eric
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