[music-dsp] achieving chiptunes sounds

Alan Wolfe alan.wolfe at gmail.com
Tue Dec 21 01:40:58 EST 2010

Hey Guys,

I'm making a programmable synth type PC program, and was playing
around with trying to make some sounds that sounded "8 bit" (ie like
NES, etc).

My program works in 32 bit floats, at 44.1khz so i tried taking my
sound samples (which are from -1 to 1), multiplying it by 128,
rounding, and then dividing by 128 so the sound waves would literally
have (aproximately) 256 possible amplitudes (and clipping off anything
above 1.0 or below -1.0)

This made almost no perceivable difference! (saw, triangle and sine
waves attempted... obviously full volume square waves are unaffected
by bit resolution LOL)

When i take it down to around 4 or lower bits THEN i hear a big
difference, but not much before then.

So then I was thinking... maybe its the sample rate?

I tried to "fake" sample rate resolution reduction by repeating
samples from the source to get the desired sample rate

like instead of having the samples go like this:

1 2 3 4 5 6 7 8 9

it might look like this:

1 1 3 4 4 6 7 7 9

if it was 1/3 the sample rate.

I tried bringing the sample rate down to 16k, 8k and 4k and it sounded
closer but still not quite right...

What is it that old system (and chiptunes) have that make them sound
so distinctly recognizable like they are?

Anyone have any tips?

Thanks!! (:

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