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Forums > C64 Composing > Digi synth/4 ch SID concept
2023-12-09 07:21
Repose

Registered: Oct 2010
Posts: 222
Digi synth/4 ch SID concept

I was thinking about digis and had an idea. Imagine playing an intro to a tune composed to use 3 channels as normal, but for two of them you swap between channel 3. On each pass, sample osc3/env3 and multiply them (and mix the 2nd pass into the first pass). You have one measure of the tune in 2 channels as samples. You can play them as a sample and then add 1 more channel like magic. The concept can be expanded to add a few more channels.
A few problems; mixing too much lowers the quality, and there could be severe aliasing due to low sample rate, and some restrictions in composition.
The advantages are the initial size is small and no complicated synth routines are needed, and it would seem like magic :)
2023-12-09 13:52
Mixer

Registered: Apr 2008
Posts: 422
Perhaps something like this?

Raveloop14.xm
2023-12-09 19:57
chatGPZ

Registered: Dec 2001
Posts: 11146
The "echo" stuff works like this too.

However, i recommend to make some actual experiments with this... it doesnt work that great unfortunately :(
2023-12-09 20:01
Repose

Registered: Oct 2010
Posts: 222
The Rave loop is pretty neat. I think compositionally, yes I imagine it would be like that. Btw, I had trouble playing that sid in 2 emulators, but I found a good copy here https://www.youtube.com/watch?v=FN6L9-TkHQ8

However, this is not exactly what I meant by my idea, as Rave had sample loops. I meant to make a tune using pure SID sounds; however those sounds are internally sampled then played back as pre-mixed samples while the freed-up voices continue to add to the composition.

It is interesting to hear how the echofied 6881 tunes work. The effect is ok.

Well, I can certainly mock up a test by simply enabling two tracks of a multi-SID tune, sampling them, then adding them back with the other tracks in an editor of some type...
2023-12-10 01:19
chatGPZ

Registered: Dec 2001
Posts: 11146
Try it... i don't expect great results from this in practise, allthough in theory it sounds awesome. Problems will be the low samplerate you can use, and the limited resolution of the sample replay.
2023-12-10 06:46
ChristopherJam

Registered: Aug 2004
Posts: 1381
Interesting idea. I suspect you'd struggle to sample one voice while playing back the layers so far at any kind of decent sample rate mind.

Still, you could optimise things quite a bit by taking advantage of things like "notes of the same duration and same envelope behaviour always produce the same stream of env3 values" - and even prewrite sets of env3 values into unrolled code that performs fast multiplies of osc3 values.

"just" doing a soft synth would perhaps be a saner route, but then again if we were sane none of us would still be using 40yo hardware :)
2023-12-10 10:05
Repose

Registered: Oct 2010
Posts: 222
Always assume something is possible, then work through the issues. You can pause sampling during the music routine, a 250uS gap (assuming a 4 line player) in sampling won't be audible.
2023-12-10 10:36
ChristopherJam

Registered: Aug 2004
Posts: 1381
Oh it wasn't the music routine I was concerned about - just the NMI playing one sample while reading another :)

Still, drop down to five or six kHz and all should be fine..
2023-12-10 11:49
Oswald

Registered: Apr 2002
Posts: 5027
instead of sampling how about putting softsynth channels into the 8bit digi "channel", or even to the 4th (1 bass, 1 drum?)
2023-12-10 14:08
ChristopherJam

Registered: Aug 2004
Posts: 1381
Oswald:
Quoting ChristopherJam
"just" doing a soft synth would perhaps be a saner route
2023-12-10 17:08
chatGPZ

Registered: Dec 2001
Posts: 11146
Quote:
You can pause sampling during the music routine, a 250uS gap (assuming a 4 line player) in sampling won't be audible.

You'll have to limit the sample rate to 4khz (every 4th line) then... so 2khz max for the signal.Oh well. Try it :)
 
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