From: pja@lk-hp-10.hut.fi (Petri Juhani Jarre)
Subject: Why GUS != synth (longish)(was: Re: Questions for GUS owners!!!)
Organization: Helsinki University of Technology, Finland
	<PJA.92Oct10123826@lk-hp-10.hut.fi> <Bvxzww.BFt@watserv1.uwaterloo.ca>
Date: 11 Oct 92 11:44:37 GMT

In article <Bvxzww.BFt@watserv1.uwaterloo.ca> ptran@sciborg.uwaterloo.ca (Phat H Tran) writes:
>   I believe the reason why other synthesizers had to combine their
>   channels for individual notes is because their library of basic
>   sounds is fixed in ROM.  To get sounds not already preset, you
>   have to mix what's already there.  With the GUS, however, its samples
>   are stored in RAM, so there is no need for it to combine multiple
>   channels to create new instruments.  Thus, it can be 32 voice
>   polyphonic under any circumstances.  (Please correct me if I'm wrong
>   regarding the mixing of presets to create new sounds.)

Waveforms in ROM are not called presets. Usually synth sounds are not
raw waveforms from memory. Combination of presets is usually called a
multi(setup) or performance or whatever depending on the manufacturer.

In a digital synth it's typical to have 1-4 DCOs (Digitally Controlled
Oscillators) which can play ROM waveforms. These waveforms are run
through DCAs (amplifiers) and DCFs (filters).  Throw in modulation
capabilities, like envelope generators for DCAs and DCFs, LFO (Low
Frequency Osc) for DCOs and DCFs. A setting of these parameters is
called a preset, which is usually stored in RAM.

What you said is basically correct. Mixing ROM waveforms is a way to
create new sounds, but it is by no means the only thing you can do -
analog synths with only three waveforms and two oscillators can do
wonderful things. Anyway, you can use the GUS or any other sound card
to sample the resulting sound and play it.

That's not the whole story, however. A sampled sound is always fixed.
For example, in a synth velocity (how hard you hit the keys) can open
filter and make a couple of the oscillators significantly louder,
aftertouch (pressing key harder when its still down) can detune one of
oscillators or make the string sample quieter and choir much louder.
And your fingertips on the modulation wheel can control the brightness
of the sound (i.e. filter cutoff).

You can sample the sound, but you can't sample the control. To
recreate the control, you need to construct the sound from its very
parts, which tends to require more than just one oscillator and other
stuff as well. And its possible to create an evolving sound which can
not sampled in its entirety with just 1M of sample RAM.

So what do I answer? Yes and no. There are sounds which can be sampled
with no loss, there are sounds that never sound the same when sampled.
What's more, sampling is copying existing sounds, synthesis is
creating new sounds. I mean typically, I'm not implying that it's a
law.

--
 Petri Jarre          !!                        It's a sky-blue sky.     
 pja@niksula.cs.hut.fi	!!                  Satellites are out tonight.     
 468 2760      	       	  !!                  Let X=X
 JMT 6 C 222b - 02150 ESPOO !!                              - Laurie Anderson
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