[sdiy] Decay

[Magnus Danielson]

From: Rönnberg Niklas <nikro at itn.liu.se>
Subject: RE: [sdiy] Decay
Date: Tue, 1 Jun 2004 20:37:30 +0200
Message-ID: <82BEDACF1CE44E45AB82F167BD8C07D1039F5C at merlin.epost.itn.liu.se>

Goder Afton Niklas,

> Well that's right, but that pot also controls the Q value and the feed back
> (right?). I would like to use the same incomming trigg pulse to control a
> similar circuit as well as a simple VCA (that is a CA3080). So I do need to
> add a decay contol on the input stage (right?). My idea is to make a snare
> drum like circuit consisting of one drum tone (like the bas drum, but
> higher pitched), a noise generator and a simple VCA. 

The good Tim Ressel is correct in pointing at this pot. Unless you require a
CV control, adjusting that pot is the right place. The decay-time of a
resonance is directly connected to it's Q-value!

The reason is that the higher Q value, the less loss of amplitude do you have
per cycle. I'm not quite sure but it is something like this:

     A
Q = ---
    /|A

where A is the amplitude and /|A is the decrease of amplitude for a single
cycle from A. If this formula is not correct, it carries about the same sense
anyway, so from a point of understanding it is still valid.

Thus, as you change the feedback, you change the Q-value and you change the
decay-time, since these are just connected together. If you would have a VCA
with a decay-curcuit controling it, that would be about the same except for
tossing more hardware on it.

Cheers,
Magnus

> Are you following me? ("Stop with that or I will have you arrested!" And
> the movie are?) Can you help me out?

Partly. Don't know. Yes, I think so.

Cheers,
Magnus