Datasette data as compressed mp3?
Posted: Mon Sep 08, 2014 8:23 am
Hi, not sure where to post this on the internet, but it tangetially relates to the VIC-20 so I'll post it here.
I have been playing around with old Roland MIDI (music) sequencers. I own an MSQ-100, which is a very early sequencer.
http://retrosynthads.blogspot.ca/2012/0 ... board.html
Because this is a one-track sequencer, it's very useful to be able to back up the memory before you overdub (and potentially make a mistake you need to undo). The sequencer was originally made to back up to an external cassette deck (like early 8-bit computers) via 1/8" headphone style connectors for "tape out" and "tape in". These are essentially D/A convertors that save the sequencer's memory as a screechy audio sound (like a telephone modem, or if you've ever played a VIC-20 datasette cassette in an audio player).
Since I don't have any portable tape decks any more I thought it would be a snap to just substitute a portable minidisc recorder walkman. I did wonder if the audio lossy compression (ATRAC) would cause me any problems. However, I supposed that since a minidisc, even thought it uses such compression, still has much better quality than even some of the best cassette decks of the 1980s (plus less wobble and flutter, and lower noise flow)....I supposed that it should therefore be able to record a simple low-baud backup easily. I even used the highest quality (lowest compression) mode of SP (Standard Play) on the minidisc recorder (this is a 256Kbps ATRAC mode).
Verifying the saved data, however, always returned a verify error.
I then got out my excellent quality SONY flash-media mp3 recorder. This is a really nice sounding device (ICD-SX712) that is capable of recording musical performances. I recorded the sequencer memory data in the highest MP3 bitrate (320kbps or something like that) to it. Again, even though it was a very high quality audio file, every attempt to verify the data returned an error.
I then set the same Sony IC flash recorder to "PCM" mode (uncompressed 44.1Khz audio - essentially .wav). This time it worked. The verify was successful. I also attempted to save to my DAT (digital audio tape uncompressed audio) recorder, and it worked again.
So, obviously, even at the highest quality, any sort of lossy audio compression (ATRAC or MP3) is destroying the integrity of the signal. Only fully uncompressed PCM audio works. I was a little surprised at this, because surely in the 1980s people were backing-up data to less than pefect cassette devices: i.e. normal Ferrous Oxide cassettes using fairly run-of-the-mill recorders that are easily matched in sound quality by today's 320Khz MP3s. I mean, even though on paper an analogue cassette is a non-lossy medium, in real practice, the high-frequency drop-off of most home consumer cassette recorders, coupled with the run-of-the-mill performance of common Fe02 (type I) cassettes was probably the same or worse than an SP minidisc or high quality MP3. Plus the noise, flutter, etc. must be worse on the cassette, whereas these artifacts are virtually absent from either minidisc or mp3.
Also, I've heard of people saving TAP and PRG files from Commodore machines as mp3 files, and hooking mp3 or CD players to the datasette port (or using a car mp3 to cassette adapter inserted into the datasette) and being successful using this method. Surely the Commodore datasette signal is more complex than the data signal from this early model sequencer, yet the audio compression doesn't seem to be destroying the signal in the case of the Commodore MP3s.
Just putting this out there for any thoughts or feedback.
I have been playing around with old Roland MIDI (music) sequencers. I own an MSQ-100, which is a very early sequencer.
http://retrosynthads.blogspot.ca/2012/0 ... board.html
Because this is a one-track sequencer, it's very useful to be able to back up the memory before you overdub (and potentially make a mistake you need to undo). The sequencer was originally made to back up to an external cassette deck (like early 8-bit computers) via 1/8" headphone style connectors for "tape out" and "tape in". These are essentially D/A convertors that save the sequencer's memory as a screechy audio sound (like a telephone modem, or if you've ever played a VIC-20 datasette cassette in an audio player).
Since I don't have any portable tape decks any more I thought it would be a snap to just substitute a portable minidisc recorder walkman. I did wonder if the audio lossy compression (ATRAC) would cause me any problems. However, I supposed that since a minidisc, even thought it uses such compression, still has much better quality than even some of the best cassette decks of the 1980s (plus less wobble and flutter, and lower noise flow)....I supposed that it should therefore be able to record a simple low-baud backup easily. I even used the highest quality (lowest compression) mode of SP (Standard Play) on the minidisc recorder (this is a 256Kbps ATRAC mode).
Verifying the saved data, however, always returned a verify error.
I then got out my excellent quality SONY flash-media mp3 recorder. This is a really nice sounding device (ICD-SX712) that is capable of recording musical performances. I recorded the sequencer memory data in the highest MP3 bitrate (320kbps or something like that) to it. Again, even though it was a very high quality audio file, every attempt to verify the data returned an error.
I then set the same Sony IC flash recorder to "PCM" mode (uncompressed 44.1Khz audio - essentially .wav). This time it worked. The verify was successful. I also attempted to save to my DAT (digital audio tape uncompressed audio) recorder, and it worked again.
So, obviously, even at the highest quality, any sort of lossy audio compression (ATRAC or MP3) is destroying the integrity of the signal. Only fully uncompressed PCM audio works. I was a little surprised at this, because surely in the 1980s people were backing-up data to less than pefect cassette devices: i.e. normal Ferrous Oxide cassettes using fairly run-of-the-mill recorders that are easily matched in sound quality by today's 320Khz MP3s. I mean, even though on paper an analogue cassette is a non-lossy medium, in real practice, the high-frequency drop-off of most home consumer cassette recorders, coupled with the run-of-the-mill performance of common Fe02 (type I) cassettes was probably the same or worse than an SP minidisc or high quality MP3. Plus the noise, flutter, etc. must be worse on the cassette, whereas these artifacts are virtually absent from either minidisc or mp3.
Also, I've heard of people saving TAP and PRG files from Commodore machines as mp3 files, and hooking mp3 or CD players to the datasette port (or using a car mp3 to cassette adapter inserted into the datasette) and being successful using this method. Surely the Commodore datasette signal is more complex than the data signal from this early model sequencer, yet the audio compression doesn't seem to be destroying the signal in the case of the Commodore MP3s.
Just putting this out there for any thoughts or feedback.