[sdiy] avrsyn update

[Daniel Kruszyna]

Jaroslaw Ziembicki <aon.912230836 at aon.at> wrote:
> I saw the code and I wonder how the filter sounds?
> A simple 8 bit arithmetics has been used. Is it really sufficient?
> Does the filter work stable?

It's not exactly hifi, but it sounds better than I expected. I was
concerned about the 8bit arithmetic as well but noticed that there
is already a spot in the code where an intermediate value is
shifted to 7bit precision. So I decided to give it a try.

It becomes unstable for small values of the control parameters. I am
trying to work around this problem with a replacement lookup table.
However, it didn't become unstable for high input frequencies, which
I've heard is usually a problem for simple digital SVFs.

I've made a couple quick samples to answer your first question.

http://krue.net/avrsyn/avrsyn-seq.ogg

Is a simple sequence with me tweaking the knobs in realtime. You can
hear a few spots where I turned the knobs too low.

http://krue.net/avrsyn/avrsyn-svf.ogg

Here, I switched the DCA to GATE mode, and used the envelope to
sweep the filter. I hope to eventually have separate envelopes.

-- Daniel