[sdiy] Basic Synth Patch? VCO-VCF-VCA

[Richard Wentk]

At 23:24 29/11/2003 -0500, Michael Boracci wrote:
>Do you think that this is something valuable? I was wondering why it is not
>done more often. Why is the oscillator fed into the filter at full volume
>and then attenuated after the fact in the classic model that is taught? I am
>speaking of the single oscillator voice of course with VCO-VCF-VCA config.

The real answer is because it's cheaper to build that way. As others have 
explained, you put the VCA at the end to keep down output noise. And since 
one VCA is a lot cheaper than two, then the best place for it is at the end 
of the chain. Don't forget you'd need a separate ADSR as well.

>You mentioned a VCO mixer which indicates attenuation before the VCF. If
>that is the case then that mixer is serving as the VCA part of
>VCO-VCA-VCF-VCA. That is how it appears to me.

In practice the amount of difference this approach makes to the sound is 
only rarely worth the extra money it would cost in a prepatched monosynth.

I can imagine that (e.g.) adding a volume spike just before filtering would 
be a good way to add an extra bite or chiff to the start of notes if the 
spike overdrove the VCF.

And in multi-oscillator synths you could add a VCA after each oscillator, 
and this way of working has its uses for some kinds of additive synthesis. 
You can also use it to create evolving semi-chords in a wavetable kind of 
way, patch in varying amounts of detuning, and so on.

But this would be considered advanced programming by many people. For most 
music the standard chain works just fine.

With a modular or a soft synth you can of course do whatever you want, and 
use the different elements you have to hand however you want to. That's 
really the whole point of a modular. :-)

Richard