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Thread: Does something like this exist - cassette emulation using sd card?

  1. #21

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    Quote Originally Posted by lowen View Post
    So, what sorts of encoder settings are you using to get 'lossless' MP3 encoding of the data audio (for that matter, which encoder; LAME, perhaps?)? (When it comes to the audio side, I do know what I'm doing; I've been a broadcast engineer for 28 years, 10 years of which was full-time, and am very familiar with variouls compression technologies and their audible effects). Which cassette data standard?
    I'm glad you're interested. My lossless method should be suitable for any two level signal, i.e. anything that switches between maximum positive and negative amplitude. So any phase and frequency modulation scheme will work as long as there's no amplitude modulation. There are some minor caveats though. Not all MP3 decoders will cope with it, such as the one Sony used in the PSP firmware which just outputs noise, and the Nitrane decoder (used in some versions of Winamp) which refuses to output anything at all. Nitrane was notoriously buggy though and Winamp dropped it for a Fraunhofer decoder at some point which works fine. Every Fraunhofer decoder I've tested works fine and fortunately they seem to be the most common. Every version of the decoder used in LAME I've tested works fine too.

    More details (over a decade old now, wow) here: https://www.worldofspectrum.org/foru...64-and-80-kbps

    If you've got any questions feel free to ask.

  2. #22

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    I use WAV for all of my vintage cassette files. I've had mixed results with MP3 and disk storage is now so plentiful, I don't bother with compression.

    Tez
    ------------------------------------------------
    My vintage collection: https://classic-computers.org.nz/collection/
    My vintage activities blog: https://www.classic-computers.org.nz/blog/
    Twitter: @classiccomputNZ ; YouTube Videos: (click here)


  3. #23

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    What about NTFS compression?

  4. #24
    Join Date
    Jun 2016
    Location
    Guisborough, England
    Posts
    155

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    Some months ago, I started messing with something like this, connected with my Epson HX-20.

    Basically, I was connecting the normal link to a cassette recorder to a laptop instead, and using the 'recorder' facility.

    This worked fine. The recording saved OK, and more importantly, the saved file could subsequently be LOADed back onto the HX.

    I found that using MP3 did work, but the process seemed less reliable. Storage is NOT a problem, so it's just not worth the risk. Using WAV format seemed totally reliable. Also, I had another motive, in that I was hoping to work ouit a way to access the saved data directly, and this would be a LOT more complicated if it was compressed.

    Someone else got involved (via an Amstrad forum) with this translation, he had done something similar with another vintage machine, and he got something working regarding READING the WAV (in effect, converting the WAV to ASCII where the data stored was in fact ASCII) but I really wanted to go a step further than that and we could not get a 'created' WAV file to be recognised by the HX. So this ground to a halt.

    However, like others, I can certainly confirm that digital devices (and I'd expect a digital recorder to work just as well as a laptop does) can replace a cassette recorder, both regarding recording the prog/data, and loading it back in again. Oh, I just used MediaPlayer to 'play' the saved file for the HX to load back in.

    Geoff

  5. #25
    Join Date
    Jan 2014
    Location
    Western North Carolina, USA
    Posts
    985

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    Quote Originally Posted by cthulhu View Post
    I'm glad you're interested. My lossless method should be suitable for any two level signal, i.e. anything that switches between maximum positive and negative amplitude. So any phase and frequency modulation scheme will work as long as there's no amplitude modulation. There are some minor caveats though. Not all MP3 decoders will cope with it, such as the one Sony used in the PSP firmware which just outputs noise, and the Nitrane decoder (used in some versions of Winamp) which refuses to output anything at all. Nitrane was notoriously buggy though and Winamp dropped it for a Fraunhofer decoder at some point which works fine. Every Fraunhofer decoder I've tested works fine and fortunately they seem to be the most common. Every version of the decoder used in LAME I've tested works fine too.

    More details (over a decade old now, wow) here: https://www.worldofspectrum.org/foru...64-and-80-kbps

    If you've got any questions feel free to ask.
    A very interesting, if specialized, technique; 'creative clipping' if you will. I'm not familiar enough with the Spectrum's cassette encoding to know if it's similar to other systems. Some systems likely do have some amplitude variations that are part of the coding, but most are simply frequency-shift-keying, which by definition has no AM components.

    But the solution I suggest, an Edirol R-09 or similar, can record and play back and act as a near-perfect cassette emulation (the only imperfection is the lack of the aux motor control to start or stop the recording and playback. You can then pull the WAV files from the recorder either over USB or via the SD card.
    --
    Bughlt: Sckmud
    Shut her down Scotty, she's sucking mud again!

  6. #26

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    I should note that if you don't care about the losslessness you can skip or undo the volume scale factor adjustment (MP3Gain) part of the process to get MP3s that any decoder should cope with perfectly. The nice thing about the losslessness though is that it makes it trivial to determine if a MP3 file will actually load correctly since if the source WAV file is known to be good then so will the MP3 generated from it as it's guaranteed to match it exactly once decoded, provided you use a good decoder. This is only really an advantage during the creation and verification part of the MP3 encoding/decoding process, it doesn't matter for the playback part as it's not like the computer loading the file will care.

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