Vincent Joguin wrote:
At 16:29 15/03/2004 +0100, you wrote:

The C64 tapes I’ve sampled myself worked when done in mono but would give me loading errors if I tried stereo, so I would not recommend using stereo for anything. Can’t say I’m for or against 8-bit or 16-bit, I guess the best thing to do is some trial and error. J

Yes, stereo is not good for extraction, but with a stereo file, the left and right mono channels can be extracted individually. I'm not talking about a simple stereo -> mono convertion that will mix both channels, which is not good. I'd say more data is always better than less, if they are properly handled.

For C64, Apple, Atari, Spectrum, etc. tapes, if you are NOT going to post-process them, it is usually best to archive them as full quality (ideally 24-bit 48KHz stereo but 16-bit 44KHz stereo will work too). Stereo is mandatory because the tape player you're playing from may have drift or "bleed" that you may not initially notice. Drift may be audible in one channel but not the other, so you'll have both channels to compare with.

The 100% best archival method of computer-encoded tapes is actually this:

1. Dump tape using best quality
2. Convert to .tape file (or whatever is appropriate for your emulator). This is done by running the .WAV through a converter appropriate for your emu. Massaging the file may be necessary for a good convert if the tape quality is terrible.
3. Play the .tape file in your emu to make sure it converted properly (although many tape formats have crude CRC checking so this may not be necessary).
4. Convert .tape file BACK TO .WAV. The result will be a digitally perfect 22KHz mono file, 8- or 16-bit, that can easily be compressed losslessly via any archival program (it's essentially square waves).

Now if you want to archive any old analog tape, the format should be 24-bit 44.1KHz or 48KHz stereo. 24-bit is necessary because analog tape does indeed contain that kind of dynamic range. If your card supports 48KHz, record in that, because cards that support 48KHz run at 48KHz natively (and may not do as good a job recording at 44.1 as you would get recording at 48 and resampling down to 44.1).

Dolby: If the tape was encoded with Dolby B or C, make sure that the Dolby B or C feature is *ON* BEFORE you start playing the tape. This is because Dolby noise reduction works, in a nutshell, by adding high-frequency information to the tape at the factory then removing that same information at the user's tape player. Otherwise, you'll be recording much high-frequency information that isn't actually signal.

Also, in case you didn't know, don't turn on Dolby noise reduction if you aren't playing a tape processed in Dolby (should be marked with "Dolby B" or "Dolby C" specifically, other generic Dolby marks need not apply).

Any questions to the above, feel free to ask me. I've been doing digital audio on personaly computers and semi-professionally since 1988.
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