Analogue systems

Why not just tune the other osc an octave higher?

If you want the RATE of vc to be 2x more, this is another story.  Lets say
at the bottom of the keyboard you want unisons and at the top of the
keyboard, you want twice the effect of 1v/oct on one of the oscillators.
You can do this by putting the VC of the second one not into the 1v/oct
input, but the other one which has an attenuator which (I believe) goes up
double from 1v/oct.


Composer Barry Schrader did a variation of this patch on most of his analog
work.  The Buchla he used had 10 dual oscillators and on-board voltage
processing on each VC input.  He would tune the osc in unison, and into one
of the 2 vc's in each, he would scale it so 1 oscillators had no VC and did
nothing, one went up one octave over the full range of VC, the third went up
2 octaves, the forth 3, the fifth 4.

Into the second VC of each oscillator he would do a variation of this.
Again, the first osc had no vc.  the second would go UP an octave over the
full range of voltage.  the third would go DOWN an octave over the full
range, the forth would go UP 2, the fifth would go DOWN 2.

His work consisted of sound masses from the two distinct VCs going into
these oscillators  Some extrememly interesting stuff came from this.  SOme
of it will be re-released next year on CD on the Innova label I believe.
Look for a piece called Trinity and another Lost Atlantis.  This routine is
all over those works and they are terrific!

best,

Peter Grenader



Tim Stinchcombe <timothy@tstinchcombe.freeserve.co.uk>wrote:

Hi Arnauld,

> I'm just looking for a trick to tune 2 VCO so that their
frequencies are
> multiples (for example, the 1st freq is F and the 2nd is 3*F).
> Any idea ?

With the '1V/octave' system used by virtually everyone these days,
this is very simple: all you need to do is add a constant voltage
offset to the second oscillator, and the ratios of the frequencies
will always be the same. For your example of 'x3', assuming you have
a CV derived from a keyboard, then add 1.58V to it to feed the second
oscillator (using a CV mixer)- it will then give you frequencies 3
times the first osc as you go up and down the keyboard (so it may
sound a little weird...).

The '1.58V' is log_2(3) (where 'log_2' is 'logs to the base 2'), so
2^1.58 = 3. You can calculate the voltage offset for other ratios 'y'
using

log_2(y) = log_10(y)/log_10(2).

If you want a more detailed explanation of the maths, let me know
(it's reasonably straightforward, as long as your 'logs' are up to
it!).

Tim
(who doesn't have any Analogue Systems stuff, just being nosey from
the Doepfer group!)




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