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From: maverick@fir.Berkeley.EDU (Vance Maverick)
Newsgroups: comp.music
Subject: Re: Additive Synthesis
Message-ID: <8528@pasteur.Berkeley.EDU>
Date: 5 Nov 90 17:50:24 GMT
References: <1990Nov5.155309.466@ccu.umanitoba.ca>
Sender: news@pasteur.Berkeley.EDU
Reply-To: maverick@fir.Berkeley.EDU (Vance Maverick)
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	If I read you right, you're asking "How do I make a bunch of partials
sound like two notes at the same pitch?"  Well, there are several cues
we use to fuse partials together into a single tone-percept.
	One of these is the harmonic-series property, which will obviously hold
for all the partials if you're doing straight naive additive synthesis. 
The chorus effect on the Synclavier (and doubtless other additive
systems) is created by a second set of harmonics, all based on a
fundamental at some ratio to the nominal fundamental of the note you
play.  To my ear, this sounds less like a doubling than like a fattening.
	There's another cue you can use, which Stephen McAdams calls
"micromodulation":  suppose you pick a random bunch of sine tones.  They
won't sound like much if they just play steadily, but if you impose on
them all the same faint frequency wobble (multiplicative in frequency),
they will group together much more strongly.  So if you have two
identical sets of harmonics, but impose on them two different wobbles,
you can cause them to group into two notes.  Check Stephen Handel's book
"Listening" for more of this material, and some advice on frequency and
degree of modulation.

	-- Vance