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Partially OT: WAV file processing question

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  • Richard A. Cini
    All: I¹ve been asked to add direct support for WAV file images of real Altair cassette tapes in the Altair32 Emulator. Essentially a WAV file, minus the
    Message 1 of 12 , Nov 24, 2008
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      Partially OT: WAV file processing question All:

          I’ve been asked to add direct support for WAV file images of real Altair cassette tapes in the Altair32 Emulator. Essentially a WAV file, minus the header, is a series of numbers that represent the sample. Since the sample is 8-bit monaural, each sample is just one byte. The sampling frequency is 22.050kHz. The recording is 124 seconds long, so there are about 2.7 million samples. The 88-ACR used a 2400Hz/1850Hz tone pair to represent logic 1 and 0, respectively. In the end, I need to turn these samples into live bits and bytes.

          I’m not exactly sure where to start with this programming project. Has anyone on-list ever done this kind of software audio processing? Basically the audio segment of the board has some signal conditioning and an XR210 FSK demodulator.

          Any help would be appreciated. Thanks.

      Rich

      --
      Rich Cini
      Collector of Classic Computers
      Build Master and lead engineer, Altair32 Emulator
      http://www.altair32.com
      http://www.classiccmp.org/cini
    • Bryan Pope
      ... Rich, Maybe the source for Tape 64 (available here: http://www.zimmers.net/anonftp/pub/cbm/transfer/datassette/index.html , then scroll down) will help? It
      Message 2 of 12 , Nov 24, 2008
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        Richard A. Cini wrote:
        > All:
        >
        > I’ve been asked to add direct support for WAV file images of real
        > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
        > file, minus the header, is a series of numbers that represent the
        > sample. Since the sample is 8-bit monaural, each sample is just one
        > byte. The sampling frequency is 22.050kHz. The recording is 124
        > seconds long, so there are about 2.7 million samples. The 88-ACR used
        > a 2400Hz/1850Hz tone pair to represent logic 1 and 0, respectively. In
        > the end, I need to turn these samples into live bits and bytes.
        >
        > I’m not exactly sure where to start with this programming project. Has
        > anyone on-list ever done this kind of software audio processing?
        > Basically the audio segment of the board has some signal conditioning
        > and an XR210 FSK demodulator.
        >
        > Any help would be appreciated. Thanks.
        >
        Rich,

        Maybe the source for Tape 64 (available here:
        http://www.zimmers.net/anonftp/pub/cbm/transfer/datassette/index.html ,
        then scroll down) will help? It is used to convert WAV files to TAP
        format used by C64 emulators.

        Cheers,

        Bryan
      • Richard A. Cini
        Bryan: I actually ran into a mirror of this somewhere which only had a subset of these programs. The issue is that most of the Commodore utilities (like mtap)
        Message 3 of 12 , Nov 24, 2008
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          Bryan:

          I actually ran into a mirror of this somewhere which only had a subset
          of these programs. The issue is that most of the Commodore utilities (like
          mtap) won't work because the C2N has the ADC in it so the software only has
          to read a pulse train.

          TurboTapeLoader looks promising but the source is in TurboPascal and
          Pascal is a language I don't know.

          KimTape looks promising as it uses 8-bit 22k samples. I'm going to look
          at this one. Tape64 looks very promising as well.

          Thanks for the pointer.

          Rich


          On 11/24/08 8:14 PM, "Bryan Pope" <bryan.pope@...> wrote:

          > Richard A. Cini wrote:
          >> All:
          >>
          >> I¹ve been asked to add direct support for WAV file images of real
          >> Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
          >> file, minus the header, is a series of numbers that represent the
          >> sample. Since the sample is 8-bit monaural, each sample is just one
          >> byte. The sampling frequency is 22.050kHz. The recording is 124
          >> seconds long, so there are about 2.7 million samples. The 88-ACR used
          >> a 2400Hz/1850Hz tone pair to represent logic 1 and 0, respectively. In
          >> the end, I need to turn these samples into live bits and bytes.
          >>
          >> I¹m not exactly sure where to start with this programming project. Has
          >> anyone on-list ever done this kind of software audio processing?
          >> Basically the audio segment of the board has some signal conditioning
          >> and an XR210 FSK demodulator.
          >>
          >> Any help would be appreciated. Thanks.
          >>
          > Rich,
          >
          > Maybe the source for Tape 64 (available here:
          > http://www.zimmers.net/anonftp/pub/cbm/transfer/datassette/index.html ,
          > then scroll down) will help? It is used to convert WAV files to TAP
          > format used by C64 emulators.
          >
          > Cheers,
          >
          > Bryan
          >
          >
          > ------------------------------------
          >
          > Yahoo! Groups Links
          >
          >
          >

          Rich

          --
          Rich Cini
          Collector of Classic Computers
          Build Master and lead engineer, Altair32 Emulator
          http://www.altair32.com
          http://www.classiccmp.org/cini
        • Bill Degnan
          ... Rich, I plan to work on this project independently, from a sound engineer perspective. I will let you know how it goes. I could be wrong, but I believe
          Message 4 of 12 , Nov 24, 2008
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            >
            > Richard A. Cini wrote:
            > > All:
            > >
            > > I've been asked to add direct support for WAV file images of real
            > > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
            > > file, minus the header, is a series of numbers that represent the
            > > sample. Since the sample is 8-bit monaural, each sample is just one
            > > byte. The sampling frequency is 22.050kHz. The recording is 124
            > > seconds long, so there are about 2.7 million samples. The 88-ACR used
            > > a 2400Hz/1850Hz tone pair to represent logic 1 and 0, respectively. In
            > > the end, I need to turn these samples into live bits and bytes.
            > >
            > > I'm not exactly sure where to start with this programming project. Has
            > > anyone on-list ever done this kind of software audio processing?
            > > Basically the audio segment of the board has some signal conditioning
            > > and an XR210 FSK demodulator.
            > >
            > > Any help would be appreciated. Thanks.
            > >

            Rich,

            I plan to work on this project independently, from a sound engineer perspective. I will let you know how it goes. I could be wrong, but I believe it's more the levels/mix than the sample rate. There is nothing wrong with over-sampling the sound source. The master of any program on tape was usually a record album. I wonder if the original BASIC record albums exist.

            BIll
          • Jim Scheef
            Rich and Bill, This is an interesting project. From a programming standpoint on a PC maybe it would be good to write a program that can read and process a
            Message 5 of 12 , Nov 25, 2008
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              Rich and Bill,

              This is an interesting project. From a programming standpoint on a PC
              maybe it would be good to write a program that can read and process a
              standard WAV file but swallow the header and trailer info in the WAV and
              just pass on the data part to the "Altair". The reverse might be useful
              as well - to accept the data sounds and output a standard WAV.

              Rich, Pascal is obtuse because the code is "upside down". Pascal
              requires that a subroutine be defined before it can be referenced.
              Pretend the code is VB but read each section starting at the bottom of
              the listing (where program flow actually begins) and it will make more
              sense.

              Jim

              Bill Degnan wrote:
              >
              >
              >
              > >
              > > Richard A. Cini wrote:
              > > > All:
              > > >
              > > > I've been asked to add direct support for WAV file images of real
              > > > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
              > > > file, minus the header, is a series of numbers that represent the
              > > > sample. Since the sample is 8-bit monaural, each sample is just one
              > > > byte. The sampling frequency is 22.050kHz. The recording is 124
              > > > seconds long, so there are about 2.7 million samples. The 88-ACR used
              > > > a 2400Hz/1850Hz tone pair to represent logic 1 and 0, respectively. In
              > > > the end, I need to turn these samples into live bits and bytes.
              > > >
              > > > I'm not exactly sure where to start with this programming project. Has
              > > > anyone on-list ever done this kind of software audio processing?
              > > > Basically the audio segment of the board has some signal conditioning
              > > > and an XR210 FSK demodulator.
              > > >
              > > > Any help would be appreciated. Thanks.
              > > >
              >
              > Rich,
              >
              > I plan to work on this project independently, from a sound engineer
              > perspective. I will let you know how it goes. I could be wrong, but I
              > believe it's more the levels/mix than the sample rate. There is nothing
              > wrong with over-sampling the sound source. The master of any program on
              > tape was usually a record album. I wonder if the original BASIC record
              > albums exist.
              >
              > BIll
              >
              >
            • Bill Degnan
              What I was planning on doing is playing actual tapes (experimenting first with newly recorded tape programs using a new tape desk (TRS 80 or Commodore) into a
              Message 6 of 12 , Nov 25, 2008
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                What I was planning on doing is playing actual tapes (experimenting first
                with newly recorded tape programs using a new tape desk (TRS 80 or
                Commodore) into a mixing board and recording studio software (ie. Cakewalk,
                etc). Doing so will isolate the sound waves for analysis. You can still
                get the old style cassette players from Radio Shack, with the REM/MIC/AUX
                inputs.

                Once captured I can clean up the data. What makes this "easy" is that it's
                not music; it's just pulses at specific frequencies within a specific
                timing. With modern studio software I can alter adjust and clean up the
                sound visually. I can also save iterations of the sound until I get it
                right. Lastly, I can mix down a clean copy to another tape. If the copy
                works, we have a process! Taken a step further, one should be able to text
                copies of program listings and convert them into sound pulses for cassette
                use.

                I have most of the Altair BASIC original versions on tape, and I really
                need to back them up.

                I also have an old tape to tape copier system used specifically for
                cassette programs. This unit needs servicing however.

                Bill

                -------- Original Message --------
                > From: "Jim Scheef" <scheefj@...>
                > Sent: Tuesday, November 25, 2008 2:54 PM
                > To: midatlanticretro@yahoogroups.com
                > Subject: Re: [midatlanticretro] Partially OT: WAV file processing
                question
                >
                > Rich and Bill,
                >
                > This is an interesting project. From a programming standpoint on a PC
                > maybe it would be good to write a program that can read and process a
                > standard WAV file but swallow the header and trailer info in the WAV and

                > just pass on the data part to the "Altair". The reverse might be useful
                > as well - to accept the data sounds and output a standard WAV.
                >
                > Rich, Pascal is obtuse because the code is "upside down". Pascal
                > requires that a subroutine be defined before it can be referenced.
                > Pretend the code is VB but read each section starting at the bottom of
                > the listing (where program flow actually begins) and it will make more
                > sense.
                >
                > Jim
                >
                > Bill Degnan wrote:
                > >
                > >
                > >
                > > >
                > > > Richard A. Cini wrote:
                > > > > All:
                > > > >
                > > > > I've been asked to add direct support for WAV file images of real
                > > > > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
                > > > > file, minus the header, is a series of numbers that represent the
                > > > > sample. Since the sample is 8-bit monaural, each sample is just
                one
                > > > > byte. The sampling frequency is 22.050kHz. The recording is 124
                > > > > seconds long, so there are about 2.7 million samples. The 88-ACR
                used
                > > > > a 2400Hz/1850Hz tone pair to represent logic 1 and 0,
                respectively. In
                > > > > the end, I need to turn these samples into live bits and bytes.
                > > > >
                > > > > I'm not exactly sure where to start with this programming project.
                Has
                > > > > anyone on-list ever done this kind of software audio processing?
                > > > > Basically the audio segment of the board has some signal
                conditioning
                > > > > and an XR210 FSK demodulator.
                > > > >
                > > > > Any help would be appreciated. Thanks.
                > > > >
                > >
                > > Rich,
                > >
                > > I plan to work on this project independently, from a sound engineer
                > > perspective. I will let you know how it goes. I could be wrong, but I
                > > believe it's more the levels/mix than the sample rate. There is nothing

                > > wrong with over-sampling the sound source. The master of any program on

                > > tape was usually a record album. I wonder if the original BASIC record

                > > albums exist.
                > >
                > > BIll
                > >
                > >
                >
                > ------------------------------------
                >
                > Yahoo! Groups Links
                >
                >
                >
              • Jim Scheef
                Bill, I like the idea of using music editing software to clean up the sound. I suppose you could create original program sound files using samples of the
                Message 7 of 12 , Nov 25, 2008
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                  Bill,

                  I like the idea of using music editing software to clean up the sound. I
                  suppose you could create original program sound files using samples of
                  the sounds at each frequency and then "programming" the output in MIDI
                  (very short notes). While probably not desirable, practical or even
                  logical, I think it would be *possible*.

                  Jim

                  Bill Degnan wrote:
                  >
                  >
                  > What I was planning on doing is playing actual tapes (experimenting first
                  > with newly recorded tape programs using a new tape desk (TRS 80 or
                  > Commodore) into a mixing board and recording studio software (ie. Cakewalk,
                  > etc). Doing so will isolate the sound waves for analysis. You can still
                  > get the old style cassette players from Radio Shack, with the REM/MIC/AUX
                  > inputs.
                  >
                  > Once captured I can clean up the data. What makes this "easy" is that it's
                  > not music; it's just pulses at specific frequencies within a specific
                  > timing. With modern studio software I can alter adjust and clean up the
                  > sound visually. I can also save iterations of the sound until I get it
                  > right. Lastly, I can mix down a clean copy to another tape. If the copy
                  > works, we have a process! Taken a step further, one should be able to text
                  > copies of program listings and convert them into sound pulses for cassette
                  > use.
                  >
                  > I have most of the Altair BASIC original versions on tape, and I really
                  > need to back them up.
                  >
                  > I also have an old tape to tape copier system used specifically for
                  > cassette programs. This unit needs servicing however.
                  >
                  > Bill
                  >
                  > -------- Original Message --------
                  > > From: "Jim Scheef" <scheefj@... <mailto:scheefj%40netscape.net>>
                  > > Sent: Tuesday, November 25, 2008 2:54 PM
                  > > To: midatlanticretro@yahoogroups.com
                  > <mailto:midatlanticretro%40yahoogroups.com>
                  > > Subject: Re: [midatlanticretro] Partially OT: WAV file processing
                  > question
                  > >
                  > > Rich and Bill,
                  > >
                  > > This is an interesting project. From a programming standpoint on a PC
                  > > maybe it would be good to write a program that can read and process a
                  > > standard WAV file but swallow the header and trailer info in the WAV and
                  >
                  > > just pass on the data part to the "Altair". The reverse might be useful
                  > > as well - to accept the data sounds and output a standard WAV.
                  > >
                  > > Rich, Pascal is obtuse because the code is "upside down". Pascal
                  > > requires that a subroutine be defined before it can be referenced.
                  > > Pretend the code is VB but read each section starting at the bottom of
                  > > the listing (where program flow actually begins) and it will make more
                  > > sense.
                  > >
                  > > Jim
                  > >
                  > > Bill Degnan wrote:
                  > > >
                  > > >
                  > > >
                  > > > >
                  > > > > Richard A. Cini wrote:
                  > > > > > All:
                  > > > > >
                  > > > > > I've been asked to add direct support for WAV file images of real
                  > > > > > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
                  > > > > > file, minus the header, is a series of numbers that represent the
                  > > > > > sample. Since the sample is 8-bit monaural, each sample is just
                  > one
                  > > > > > byte. The sampling frequency is 22.050kHz. The recording is 124
                  > > > > > seconds long, so there are about 2.7 million samples. The 88-ACR
                  > used
                  > > > > > a 2400Hz/1850Hz tone pair to represent logic 1 and 0,
                  > respectively. In
                  > > > > > the end, I need to turn these samples into live bits and bytes.
                  > > > > >
                  > > > > > I'm not exactly sure where to start with this programming project.
                  > Has
                  > > > > > anyone on-list ever done this kind of software audio processing?
                  > > > > > Basically the audio segment of the board has some signal
                  > conditioning
                  > > > > > and an XR210 FSK demodulator.
                  > > > > >
                  > > > > > Any help would be appreciated. Thanks.
                  > > > > >
                  > > >
                  > > > Rich,
                  > > >
                  > > > I plan to work on this project independently, from a sound engineer
                  > > > perspective. I will let you know how it goes. I could be wrong, but I
                  > > > believe it's more the levels/mix than the sample rate. There is
                  > nothing
                  >
                  > > > wrong with over-sampling the sound source. The master of any
                  > program on
                  >
                  > > > tape was usually a record album. I wonder if the original BASIC record
                  >
                  > > > albums exist.
                  > > >
                  > > > BIll
                  > > >
                  > > >
                  > >
                  > > ------------------------------------
                  > >
                  > > Yahoo! Groups Links
                  > >
                  > >
                  > >
                  >
                  >
                • Richard A. Cini
                  Guys: I did some research today. I would prefer working directly with sound card samples only because that¹s how most normal people are going to produce WAV
                  Message 8 of 12 , Nov 25, 2008
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                    Re: [midatlanticretro] Partially OT: WAV file processing question Guys:

                        I did some research today. I would prefer working directly with sound card samples only because that’s how most normal people are going to produce WAV files (not that you’re not normal Bill...). It’s easy to strip the WAV header using a program called Wav2Pcm (code available in the ether). There is something called a Goertzel transform which is a modified FFT whose purpose is to zero-in on a specific frequency. If I couple that with a type of a bandpass filter, I think I can tease out the 1850Hz and 2400Hz signals which represent logic 0 and 1, respectively.

                        The tape sample I have is 8-bit mono at 11.025kHz, but most of the other sample stuff I’m working with is 16-bit mono at 44.1kHz.

                    Rich


                    On 11/25/08 5:41 PM, "Jim Scheef" <scheefj@...> wrote:


                     

                    Bill,

                    I like the idea of using music editing software to clean up the sound. I
                    suppose you could create original program sound files using samples of
                    the sounds at each frequency and then "programming" the output in MIDI
                    (very short notes). While probably not desirable, practical or even
                    logical, I think it would be *possible*.

                    Jim

                    Bill Degnan wrote:
                    >
                    >
                    > What I was planning on doing is playing actual tapes (experimenting first
                    > with newly recorded tape programs using a new tape desk (TRS 80 or
                    > Commodore) into a mixing board and recording studio software (ie. Cakewalk,
                    > etc). Doing so will isolate the sound waves for analysis. You can still
                    > get the old style cassette players from Radio Shack, with the REM/MIC/AUX
                    > inputs.
                    >
                    > Once captured I can clean up the data. What makes this "easy" is that it's
                    > not music; it's just pulses at specific frequencies within a specific
                    > timing. With modern studio software I can alter adjust and clean up the
                    > sound visually. I can also save iterations of the sound until I get it
                    > right. Lastly, I can mix down a clean copy to another tape. If the copy
                    > works, we have a process! Taken a step further, one should be able to text
                    > copies of program listings and convert them into sound pulses for cassette
                    > use.
                    >
                    > I have most of the Altair BASIC original versions on tape, and I really
                    > need to back them up.
                    >
                    > I also have an old tape to tape copier system used specifically for
                    > cassette programs. This unit needs servicing however.
                    >
                    > Bill
                    >
                    > -------- Original Message --------
                    >  > From: "Jim Scheef" <scheefj@... <mailto:scheefj%40netscape.net>  <mailto:scheefj%40netscape.net>>
                    >  > Sent: Tuesday, November 25, 2008 2:54 PM
                    >  > To: midatlanticretro@yahoogroups.com <mailto:midatlanticretro%40yahoogroups.com>  
                    > <mailto:midatlanticretro%40yahoogroups.com>
                    >  > Subject: Re: [midatlanticretro] Partially OT: WAV file processing
                    > question
                    >  >
                    >  > Rich and Bill,
                    >  >
                    >  > This is an interesting project. From a programming standpoint on a PC
                    >  > maybe it would be good to write a program that can read and process a
                    >  > standard WAV file but swallow the header and trailer info in the WAV and
                    >
                    >  > just pass on the data part to the "Altair". The reverse might be useful
                    >  > as well - to accept the data sounds and output a standard WAV.
                    >  >
                    >  > Rich, Pascal is obtuse because the code is "upside down". Pascal
                    >  > requires that a subroutine be defined before it can be referenced.
                    >  > Pretend the code is VB but read each section starting at the bottom of
                    >  > the listing (where program flow actually begins) and it will make more
                    >  > sense.
                    >  >
                    >  > Jim
                    >  >
                    >  > Bill Degnan wrote:
                    >  > >
                    >  > >
                    >  > >
                    >  > > >
                    >  > > > Richard A. Cini wrote:
                    >  > > > > All:
                    >  > > > >
                    >  > > > > I've been asked to add direct support for WAV file images of real
                    >  > > > > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
                    >  > > > > file, minus the header, is a series of numbers that represent the
                    >  > > > > sample. Since the sample is 8-bit monaural, each sample is just
                    > one
                    >  > > > > byte. The sampling frequency is 22.050kHz. The recording is 124
                    >  > > > > seconds long, so there are about 2.7 million samples. The 88-ACR
                    > used
                    >  > > > > a 2400Hz/1850Hz tone pair to represent logic 1 and 0,
                    > respectively. In
                    >  > > > > the end, I need to turn these samples into live bits and bytes.
                    >  > > > >
                    >  > > > > I'm not exactly sure where to start with this programming project.
                    > Has
                    >  > > > > anyone on-list ever done this kind of software audio processing?
                    >  > > > > Basically the audio segment of the board has some signal
                    > conditioning
                    >  > > > > and an XR210 FSK demodulator.
                    >  > > > >
                    >  > > > > Any help would be appreciated. Thanks.
                    >  > > > >
                    >  > >
                    >  > > Rich,
                    >  > >
                    >  > > I plan to work on this project independently, from a sound engineer
                    >  > > perspective. I will let you know how it goes. I could be wrong, but I
                    >  > > believe it's more the levels/mix than the sample rate. There is
                    > nothing
                    >
                    >  > > wrong with over-sampling the sound source. The master of any
                    > program on
                    >
                    >  > > tape was usually a record album. I wonder if the original BASIC record
                    >
                    >  > > albums exist.
                    >  > >
                    >  > > BIll
                    >  > >
                    >  > >
                    >  >
                    >  > ------------------------------------
                    >  >
                    >  > Yahoo! Groups Links
                    >  >
                    >  >
                    >  >
                    >
                    >
                     
                        


                    Rich

                    --
                    Rich Cini
                    Collector of Classic Computers
                    Build Master and lead engineer, Altair32 Emulator
                    http://www.altair32.com
                    http://www.classiccmp.org/cini
                  • B Degnan
                    ... Me? Recording Studio software can do all of this easily. Some of them let you write your own filters, mastering by using threshholds, etc.
                    Message 9 of 12 , Nov 25, 2008
                    • 0 Attachment
                      Richard A. Cini wrote:
                      Re: [midatlanticretro] Partially OT: WAV file processing question Guys:

                          I did some research today. I would prefer working directly with sound card samples only because that’s how most normal people are going to produce WAV files (not that you’re not normal Bill...). It’s easy to strip the WAV header using a program called Wav2Pcm (code available in the ether). There is something called a Goertzel transform which is a modified FFT whose purpose is to zero-in on a specific frequency. If I couple that with a type of a bandpass filter, I think I can tease out the 1850Hz and 2400Hz signals which represent logic 0 and 1, respectively.

                          The tape sample I have is 8-bit mono at 11.025kHz, but most of the other sample stuff I’m working with is 16-bit mono at 44.1kHz.

                      Rich

                      <xml>Me?</xml>

                      Recording Studio software can do all of this easily.  Some of them let you write your own filters, mastering by using threshholds, etc.

                      Jumping OT slightly:

                      Here is an intersting article
                      http://vintagecomputer.net/CISC367/Microtrek%20August%201976%20Super-simple%20Cassette%20Interface.pdf
                      Sort of a wah wah pedal for cassette signal processing that mimic teletype outputs and compresses the sound signal.  The compression clarifies the zero one difference.

                      bd


                    • Richard A. Cini
                      Bill: I don¹t doubt that a studio-level program could do this, but the challenge is that people who use the emulator would have to send me the raw dumps and
                      Message 10 of 12 , Nov 25, 2008
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                        Re: [midatlanticretro] Partially OT: WAV file processing question Bill:

                            I don’t doubt that a studio-level program could do this, but the challenge is that people who use the emulator would have to send me the raw dumps and I’d have to make them usable. If I build this capability programmability, then Altair32 users can open the WAV file directly. That’s really what I’m striving for (at least for now :-))

                        Rich


                        On 11/25/08 9:17 PM, "B Degnan" <billdeg@...> wrote:
                        Richard A. Cini wrote:
                        Re: [midatlanticretro] Partially OT: WAV file processing question Guys:
                         
                            I did some research today. I would prefer working directly with sound card samples only because that’s how most normal people are going to produce WAV files (not that you’re not normal Bill...). It’s easy to strip the WAV header using a program called Wav2Pcm (code available in the ether). There is something called a Goertzel transform which is a modified FFT whose purpose is to zero-in on a specific frequency. If I couple that with a type of a bandpass filter, I think I can tease out the 1850Hz and 2400Hz signals which represent logic 0 and 1, respectively.
                         
                            The tape sample I have is 8-bit mono at 11.025kHz, but most of the other sample stuff I’m working with is 16-bit mono at 44.1kHz.
                         
                        Rich
                         

                        <xml>Me?</xml>

                        Recording Studio software can do all of this easily.  Some of them let you write your own filters, mastering by using threshholds, etc.

                        Jumping OT slightly:

                        Here is an intersting article
                        http://vintagecomputer.net/CISC367/Microtrek%20August%201976%20Super-simple%20Cassette%20Interface.pdf
                        Sort of a wah wah pedal for cassette signal processing that mimic teletype outputs and compresses the sound signal.  The compression clarifies the zero one difference.

                        bd


                        Rich

                        --
                        Rich Cini
                        Collector of Classic Computers
                        Build Master and lead engineer, Altair32 Emulator
                        http://www.altair32.com
                        http://www.classiccmp.org/cini
                      • B Degnan
                        Ah. I am most interested in the tape2wav part, producing good copy-able wavs that can be used as masters for reproduction. bd ... From: Richard A. Cini
                        Message 11 of 12 , Nov 25, 2008
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                          Re: [midatlanticretro] Partially OT: WAV file processing questionAh. I am most interested in the tape2wav part, producing good copy-able wavs that can be used as masters for reproduction.

                          bd



                          From: Richard A. Cini <rcini@...>
                          Sent: Tuesday, November 25, 2008 9:37 PM
                          To: midatlanticretro@yahoogroups.com <midatlanticretro@yahoogroups.com>
                          Subject: Re: [midatlanticretro] Partially OT: WAV file processing question

                          Bill:

                              I don’t doubt that a studio-level program could do this, but the challenge is that people who use the emulator would have to send me the raw dumps and I’d have to make them usable. If I build this capability programmability, then Altair32 users can open the WAV file directly. That’s really what I’m striving for (at least for now :-))

                          Rich


                          On 11/25/08 9:17 PM, "B Degnan" <billdeg@...> wrote:
                          Richard A. Cini wrote:
                          Re: [midatlanticretro] Partially OT: WAV file processing question Guys:
                           
                              I did some research today. I would prefer working directly with sound card samples only because that’s how most normal people are going to produce WAV files (not that you’re not normal Bill...). It’s easy to strip the WAV header using a program called Wav2Pcm (code available in the ether). There is something called a Goertzel transform which is a modified FFT whose purpose is to zero-in on a specific frequency. If I couple that with a type of a bandpass filter, I think I can tease out the 1850Hz and 2400Hz signals which represent logic 0 and 1, respectively.
                           
                              The tape sample I have is 8-bit mono at 11.025kHz, but most of the other sample stuff I’m working with is 16-bit mono at 44.1kHz.
                           
                          Rich
                           

                          <xml>Me?</xml>

                          Recording Studio software can do all of this easily.  Some of them let you write your own filters, mastering by using threshholds, etc.

                          Jumping OT slightly:

                          Here is an intersting article
                          http://vintagecomputer.net/CISC367/Microtrek%20August%201976%20Super-simple%20Cassette%20Interface.pdf
                          Sort of a wah wah pedal for cassette signal processing that mimic teletype outputs and compresses the sound signal.  The compression clarifies the zero one difference.

                          bd


                          Rich

                          --
                          Rich Cini
                          Collector of Classic Computers
                          Build Master and lead engineer, Altair32 Emulator
                          http://www.altair32.com
                          http://www.classiccmp.org/cini
                        • Jeffrey Brace
                          I took Pascal in college but it has been about 15 years since I have used it. I might be able to help with the Pascal. I do have books on Pascal if you want to
                          Message 12 of 12 , Nov 25, 2008
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                            I took Pascal in college but it has been about 15 years since I have used it. I might be able to help with the Pascal. I do have books on Pascal if you want to borrow them. Let me know.
                             
                            ----- Original Message -----
                            Sent: Tuesday, November 25, 2008 2:49 PM
                            Subject: Re: [midatlanticretro] Partially OT: WAV file processing question

                            Rich and Bill,

                            This is an interesting project. From a programming standpoint on a PC
                            maybe it would be good to write a program that can read and process a
                            standard WAV file but swallow the header and trailer info in the WAV and
                            just pass on the data part to the "Altair". The reverse might be useful
                            as well - to accept the data sounds and output a standard WAV.

                            Rich, Pascal is obtuse because the code is "upside down". Pascal
                            requires that a subroutine be defined before it can be referenced.
                            Pretend the code is VB but read each section starting at the bottom of
                            the listing (where program flow actually begins) and it will make more
                            sense.

                            Jim

                            Bill Degnan wrote:
                            >
                            >
                            >
                            > >
                            > > Richard A. Cini wrote:
                            > > > All:
                            > > >
                            > > > I've been asked to add direct support for WAV file images of real
                            > > > Altair cassette tapes in the Altair32 Emulator. Essentially a WAV
                            > > > file, minus the header, is a series of numbers that represent the
                            > > > sample. Since the sample is 8-bit monaural, each sample is just one
                            > > > byte. The sampling frequency is 22.050kHz. The recording is 124
                            > > > seconds long, so there are about 2.7 million samples. The 88-ACR used
                            > > > a 2400Hz/1850Hz tone pair to represent logic 1 and 0, respectively. In
                            > > > the end, I need to turn these samples into live bits and bytes.
                            > > >
                            > > > I'm not exactly sure where to start with this programming project. Has
                            > > > anyone on-list ever done this kind of software audio processing?
                            > > > Basically the audio segment of the board has some signal conditioning
                            > > > and an XR210 FSK demodulator.
                            > > >
                            > > > Any help would be appreciated. Thanks.
                            > > >
                            >
                            > Rich,
                            >
                            > I plan to work on this project independently, from a sound engineer
                            > perspective. I will let you know how it goes. I could be wrong, but I
                            > believe it's more the levels/mix than the sample rate. There is nothing
                            > wrong with over-sampling the sound source. The master of any program on
                            > tape was usually a record album. I wonder if the original BASIC record
                            > albums exist.
                            >
                            > BIll
                            >
                            >

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