Audio Cassette formats

From: John Foust <jfoust_at_threedee.com>
Date: Wed Nov 25 14:46:01 1998

Yes, there are/were many different formats for recording digital
data on audio cassettes. Some used frequency, some used phase
info, and some recorded to the tape using something other than
conventional voice-style recording. Think of them as modems
at speeds of 120 to 2400 baud.

I've found a number of decoders that were developed for the
emulator scene. Most are quite crude and unforgiving.

I concluded that I wanted to store absolutely uncompressed
digitized audio until I confirmed that any of today's various
compression methods wouldn't obliterate the encoded data.

Given the dozens of encoders and compression schemes out there,
how do you know if a particular scheme won't wipe out the
data by simplifying waveforms, fudging phase relationships, etc.?

Storage is cheap. You don't need stereo. If the waveforms use
audio in the range 1200 to 2400 Hz, for example, then Nyquist
tells you to oversample by 2 to 8 times, meaning even 8 Khz,
8-bit might be overkill with roughly 8 K/sec storage,
and 22 Khz sampling is certainly adequate.

As someone pointed out earlier in the thread, being able to tweak
the azimuth on the tape head makes all the difference with some tapes.

- John
Received on Wed Nov 25 1998 - 14:46:01 GMT