[sdiy] Mixer levels

[jhaible]

> If you combine 2 signals from the same VCO, two different waves I mean,
> they can combine in phase with each other or out of phase, was we've
> discussed before. In some cases, you actually don't add to the voltage
> swing at all.
>
> For instance, if you combine a short pulse, with a sine and they're out
> of phase you will have the sine intact, but with a rectangluar notch on
> one side. That notch willgo down to zero, but it won't add anything at
> all. Does this sound different than if that was a huge spike sticking
> off of the sine? I don't know. But one way uses up a bunch of headroom,
> probably clipping the mixer and the other wave uses the same amount of
> headroom as the sine alone.

In linear systems, this makes sense. In nonlinear systems, it will make a
huge
difference if the spike on top of the sine is rounded by soft clipping or
if the spike that's "shielded" inside the sine is unaltered.
If you're thinking "HiFi" (linear, headroom, all that stuff), two such cases
might be equivalent, or the case with higher amplitude will get additional
harmonics from distortion (when you're exceeding your headroom).
If you're thinking nonlinear, the clipped (steady) signal of a oscillator
wave
might have *less* harmonic content than the unaltered version. That's the
joy
of analogue synthesis (and quite different from what people have incorrectly
called "subtractive synthesis").

A pulse with modulated pulse width is very similar to two saw waves
which are added in a linear system (with one saw inverted, if memory
serves):
There's a constant movement and change in your sound.
If you're running the two saw waves thru a nonlinear system that clips
(or rounds) its peaks, the beating (and timbre movement) will stop
for a while, when the addition of both signals goes above the clipping
threshold. (If you cannot get higher, you won't have any movement from
going higher, either.)
This is similar to a PWM with a *clipped* sine LFO for modulation
source.
I'm not trying to show equivalence between PWM and true beating here.
I want to point out that nonlinearity can transform simple amplitude
effects into something very different: a perceived change of *modulation*.

JH.