[sdiy] harmonics & vibrato

[jhaible]

> Actually I *transformed* a patch on my Virus just by adding a touch of
> random pitch offset to each voice oscillator. Suddenly it came alive. So
it
> definitely does have its uses.

That's why I said randomizing is a good start.

But there is more. On my OB-8 some of the voices are more detuned
that others (faster beating between VCOs), and due to the voice allocation
the same amount of detuning will come every 8th key. (This is in addition
to a fluctuation that can be emulated by a random function.) On a
Prophet 5, this does *not* come every 5th key, because voices are reassigned
if you hit the same note twice. On a PS-3200, each semitone has its
own beat rate (and exactly the double beat rate one octave higher), and
octaves are beat free. Just to name a few examples. I think the ear is
very sensitive to such patterns. Detuning in an analogue polysynth is
a mix of deterministic and random effects, and the deterministic part
is often neglected.



> >Another thing to experiment: LFO with DC offset, depth (including the
> >offset part) thru a VCA, controlled by Aftertouch, and then AC-coupled
> >before it goes to the VCO. Thus a rather slowly varying force from
> >your fingertips will be superposed to the LFO's wave.
>
> Wouldn't that just distort the LFO waveshape? I'm not sure I follow this
one.

"Distorting the waveshape" is just a different way to look at it.
I would like to describe it as AM (amplitude modulation of the LFO
wave by aftertouch) plus manual modulation of the VCO frequency by
a HP-filtered force of the fingers (from the DC offset part of the LFO).

JH.