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Re: [cosmacelf] Re: Cassette tapes

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  • Lee Hart
    ... I agree. The computer itself (Elf, VIP, and other old classic computers) will probably continue to work (or remain repairable) far longer than any
    Message 1 of 39 , Dec 4, 2012
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      Kevin wrote:
      > I understand archival preservation, and I think it makes my point
      > even stronger -- cassettes won't be around, so ensure you retain a
      > digital copy that will not degrade.

      I agree. The computer itself (Elf, VIP, and other old classic computers)
      will probably continue to work (or remain repairable) far longer than
      any consumer-grade cassette tape or tape recorder. So fundamentally, we
      need some way to imitate the function of these tape recorders.

      A PC, or any computer or device that can record and playback sounds can
      (theoretically) serve this purpose. However, some are better than
      others. Many digital storage devices depend on quirks of the human ear
      to mask the shortcomings of their digitization and recreation of sound.
      You may not hear the imperfections, but the simple circuits and software
      in an old computer cares!

      > But all we really need to archive is the binary.

      That is true from a data standpoint. But you will still need some method
      to convert this binary data into the audio tones that the classic
      computer needs. Similarly, you should have a method to convert the audio
      tones the class computer produces into digital data.

      > we dont' need to keep the audio because we can easily write software
      > (either on the ELF, or on a modern PC), which can read and produce
      > new audio at will.

      Maybe *you* can write such software... but I can't! I have to depend on
      the kindness of strangers to do this kind of work.

      The problem looks simple on the surface of it. "How hard can it be?
      Those old computers were so stupid that it *can't* be that difficult to
      read/write the data they produced." Someone can slap together a program
      that sort-of works. If the data is perfect, the program has no trouble
      reading it. That's going to be good enough 90% of the time.

      The real fun begins when you try to recover an old degraded tape, one so
      bad that the original computer can't read it without errors. A
      quick-n-dirty program on a PC is *also* likely to have trouble reading it.

      > My goal is to preserve old data. Artifacts like cassettes will be
      > nice to look at in a museum and maybe someone will have a working
      > unit in the future. But ELF hobbyists need a good substitute and and
      > way to trade audio files over the Internet to share with each other.
      >
      > The solution to that is software on their PCs.

      Agreed! But, does such software exist yet? Can it take a binary or hex
      file, and produce (via the sound card) the same audio output that an Elf
      or VIP needs to load correctly.

      And, can it convert the audio output from such a computer into a binary
      or hex file?

      --
      If you want to build a ship, don't drum up people to collect wood
      and don't assign them tasks and work. Rather, teach them to long
      for the endless immensity of the sea. -- Antoine de Saint-Exupery
      --
      Lee A. Hart http://www.sunrise-ev.com/LeesEVs leeahart@...
    • joshbensadon
      Hi Herb, Surely you must have heard of the Kansas City Standard? I read an article on it in the 70 s. Some guys that met in Kansas City decided to make a
      Message 39 of 39 , Dec 5, 2012
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        Hi Herb,

        Surely you must have heard of the Kansas City Standard?
        I read an article on it in the 70's. Some guys that met in Kansas City decided to make a standard to encode bits on cassette. I don't recall the standard exactly, but it's goal is to have 1's and 0's to occupy the same amount of tape. So they did something like 4 cycles of 2400Hz for logic 1 and 2 cycles of 1200Hz for logic 0. These numbers might not be the actual values, but you can google it.

        I think I scanned this article from Popular Electronics... let me try finding it. It would be on Rich Cini's web site.

        Regards,
        Josh


        --- In cosmacelf@yahoogroups.com, "thinkpast" <hjohnson@...> wrote:
        >
        >
        >
        > --- In cosmacelf@yahoogroups.com, "Chris" <cwardell2000@> wrote:
        > >
        > > Herb,
        > >
        > > The files section contains a "Giant Board HTML" folder that has the Netronics documentation for the "Giant Board" which is what added cassette I/O to the ELF II. You will find the schematic which includes the cassette circuits and the binary code for the monitor program that includes cassette read and write routines.
        > >
        > > C.W.
        > >
        > I'm on it! Thanks. Now I have to figure out how fast the ELF II ran instructions, as that sets the rate for the 1's and 0's the cassette interface produced or reads. The docs with the Giant Board mention "like the Kansas City standard" but that may mean "an apple is a fruit like a banana". I'll add some docs and annotated code to the page linked below, maybe someone with more clues than I can help on this?
        >
        > http://www.retrotechnology.com/restore/cass_super.html
        >
        > Herb
        >
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