Analogue systems

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!)