- Joined: 05 Sep 2013
- Posts: 3828
- Location: Stockholm, Sweden
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 Posted: Sat Jan 06, 2024 1:24 pm
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I know what's PCM and PWM. What I meant is that I suspect this code really does a 1-bit PCM, no PWM or PDM of any sort. And it's not exactly the same thing.
I suspect here the source data is basically just getting the sign bit from the original wave file. 0 when the wave is positive, 1 when negative - or the other way around it doesn't really matter.
Honestly I'm not sure how can I prove this. Probably I could amplify the arcade .wav file until each single sample is either +MAX or -MAX and see if is sounds like what we get from the game...
I'll try.
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- Site Admin
- Joined: 19 Oct 1999
- Posts: 14745
- Location: London
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Posted: Sat Jan 06, 2024 1:37 pm
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That’s exactly what I did to approximate the 1-bit data when experimenting with it myself; it’s less correct than a “dithered” or “error diffusion” conversion to 1 bit, but for a few examples where I felt I had matching data, it sounded very similar to me.
For Alex Kidd: The Lost Stars, I couldn’t find a software tool that would give me the PCM data, so I approximated it by recording the output of MAME and then guessed at the approximate sample rate. I guess Sega might have used some PCM data as the input but I’m not sure how they would have done sample rate conversion.
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