basic synthesis/math question

From: Dusty Leary (dusty@freescratchtickets.com)
Date: Fri Jun 09 2000 - 02:21:02 EDT


I'm sorry to bug the people on this list this isn't saol-related, but I
can't seem to find the answer to a question online, and if anyone knows the
answer, it's the people here...

first: I am not a dsp professional... although I'm a programmer and I'm
interested in sound synthesis, it's always been more of a user-ish hobby for
me, I've never gone farther than very basic exploration in implementing
stuff

anyway, I was trying a little bit of this exploration recently... I hacked
up a quick little sound component framework thing in python, and was
outputting sounds and listening to them...

generating "normal" waves of various shapes seemed to work and sound just
fine, with a little "wave generator" component that is hardcoded to 440hz,
but selectable waveform

when this pitch is hardcoded in, the sine wave generator is like so: s(t) =
sin(2pi*440*t)

then, I try to make the pitch resolved by another input signal... so, s(t)
= sin(2pi*f(t)*t)

this works fine when the input signal is f(t) = 440, and fine when the input
signal is a square wave oscillating between 220 and 440 twice a second...

but, when I try to make the input signal a sine wave, to oscillate between
220 and 440 twice per second, things mess up...

I can understand why it's not sound right, when the output signal has all
the constants removed, it's basically s(t) = sin(x*sin(x)), and the pitch
keeps getting higher and higher

I'm a bit embarassed, because it seems like this should be simple, but I
can't think of it!

what am I doing wrong?



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