Questions about ".Wav" Files in OpenMSX.

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By sd_snatcher

Prophet (3480)

sd_snatcher's picture

06-03-2016, 18:36


Indeed. But the problem doesn't come from the data itself, but from the fact that cassette tapes are noisy by nature. Its baseline Hiss, wow and flutter will make sure that no two bits will be alike in the tape. And all that without considering the age of the media. I was impressed that it still worked.

To regenerate the Robocop tape, I used castools. First, I converted both sides of the tape from wav to cas. Then I tested the whole game to make sure everything was working (I had to reconvert two more times while fiddling with wavtocas parameters to get a fully working version).

Last, I used castowav to generate a new clean audio. The only issue about the process is that castowav generates tapes with round waves at 43KHz. It would be better if it used tms9918's idea of TTL wav files, because it's more faithful to what the real MSX does, and result in much smaller files.

I kept the original wav files just in case.

By Manuel

Ascended (18233)

Manuel's picture

06-03-2016, 19:58

openMSX itself generates square wave audio, AFAIK... so you could also save the files in openMSX again to regenerate it... a bit clumsy though Smile You could change cas2wav, it's open source, to do that too. (I guess the 'square' waves is what you meant with TTL wav files.)

By wouter_

Champion (469)

wouter_'s picture

06-03-2016, 20:59

This discussion might also be relevant. It's a request to add .TAP file support to openMSX. Very short summary: TAP is a file format that encodes the lengths of all high/low sequences in the tape. So it's able to represent every possible tape (as seen from the MSX cassette input point of view). Compared to e.g. .TSX it's a _much_much_ simpler and therefor better format.

The only real advantage these specific tape file formats have over WAV files is the smaller file size. In the above discussion some example .TAP/.WAV files were given. Those .TAP files were indeed about 35x smaller than the corresponding .WAV files. However when _both_ versions were (g)zipped, the compressed .WAV.gz was about 1.2x smaller than the compressed .TAP.gz file. And this negates the only technical advantage of those specific tape file formats (also given that many tools already do support .WAV.gz).

Earlier in this thread Grauw said that compression only works well for _clean_ WAV files. But as mentioned in the above discussion, the tool to create a clean WAV files is almost exactly the same as the existing tools to create .TAP files. So the tools do exist already.

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