[LAD] Plugin 1/oct frequency controls (AMS/MCP/VCO)

Fons Adriaensen fons at linuxaudio.org
Tue Aug 21 21:54:21 UTC 2012

On Tue, Aug 21, 2012 at 10:14:28PM +0200, Nick Copeland wrote:

> a. 1/Oct is not a reference value, it is a definition for the effects
> of amodifier signal. The value of 0.0 should definitely not refer to
> A440.When a mod signal is applied to an osc then it modifies the setting
> of the osc. You set the osc to A440 and apply 0v then it has no affect.

I agree. The only way I could maybe understand Dave's view
is as follows:

You write 'if you set and oscillator to A440'. Now *how* is 
that done ? It could be some control that is 'internal' to
the oscillator, and then all other 'voltages' are relative.
Now if that 'internal' control is actually using a port,
one *could* say that such a port has an 'absolute' meaning
for zero.

The weak part in that argumentation is that such a port
is not different from any other one that modifies the
same frequency. In the end the sum of all values is what
matters. Since adding two 'absolute' values makes no sense,
there are two ways to look at such a sum:

* One term is absolute, the other (N-1) must be relative, or
* All N are relative, being added to something absolute which
  is internal.

Since are ports are in fact equal (even if some may have 
variable gain and some not), I tend to prefer the second
way of viewing things.

Dave, this is also visible in the code: the only 'absolute'
value in the argument of exp2ap() is that constant term,
and it doesn't belong to any of the ports whose values are
being summed.



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