[linux-audio-user] 8 oscillator ecasynth

Steve Harris S.W.Harris at ecs.soton.ac.uk
Fri Sep 3 10:28:47 EDT 2004


On Thu, Sep 02, 2004 at 12:57:05 -0400, Eric Dantan Rzewnicki wrote:
> > > 3) possibly related to 2) ... There are artifacts and glitches in the 
> > > sound output. I'm not sure what to call them ... just a sort of scratchy 
> > > sound when I move the controllers. I'm not sure if this is xrun related 
> > > or not. Could it be something in the plugin itself? I'm not sure how to 
> > > sort out where the issue is.
> > Yes, its probably in the plugin, its often called "zipper noise" (it
> > sounds like someone dragging a zip), if it is that I will fix it.
> 
> Yes. I think that is it. Anything I can do to help you fix it?
> 
> In the docs you mention that the Hz control is not interpolated. Any
> chance that could be added? Is it something a novice programmer could
> try to take a whack at with a little guidance? or is it fairly involved?

Its pretty easy, at the top of the inner loop the frequency is set, but it
should be changed so that its updated every 4 or 8 samples, linearly
interpolating between the previous value and the new one.

It may needa bit of tweaking, eg. applying a lowpass filter to the
linearly interpolated parameter, but I think just linear is fine.

Its about 4 or 5 lines of code and hot hard, but tricky to explain. I'l
walk you through any problems, offlist if you want to try it.
 
> Are the value ranges for the warmth and stability controls 0.0-1.0? 
> I think I see in the code where warm is clamped:
> osc->nyquist = fs * (0.47f - f_clamp(warm, 0.0f, 1.0f) * 0.41f);
> but, can't make out just what happens with stability...

Its a bit too icky to explain, yes thier both [0,1].

- Steve


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