Dave Smith Instruments SYNTHESIZERS

From: "dhamaryder" <dhamaryder@...>

> Hi guys,  There's something i don't really get.  Does anybody
> know why if you have an LFO modulating the Delay time of any of
> the delays it modulates the pitch in strange ways. I don't get the
> connection. Maybe I'm missing some basic law of synthesis or
> something.  Not that I can't use the effect but I'm just not
> undestanding why it happens.
>
imagine this:
you have an array of samples, and you go through this playing back one after
the other... when you get to then end, you go back to the first sample...
this array is a fixed length, but you can control the speed at which you
move through it in order to change the length of time per cycle....

now imagine:
your delay line has a fixed frequency sine wave stored in it.

now imagine:
as you are playing back through the delay line, you are changing the SPEED
at which you move throutgh the delay line (like for instance with an LFO) so
the frequency of the "sine wave" at the output of the delayline is now
varying as the LFO changes the speed at which it is read back...

You have just imagined the way that the output of the delay line in your
evolver works, and seen, in you mind, the way that the pitch of a static
oscillator gets shifted in a moulated delay line....


Of course, in the delay line, after reading a sample, you also write a new
one back in its place (which is the sum of the output of the delay line and
the current oscillator output position) so you actually have what you are
playing entering the delay line as you play it, as well as older sounds
repeating. but any difference in the speed you are moving through it between
the time a sample is going in, and when it comes out results in the delay
line sample having a different pitch to the original sample.



julian