[PD] random oscillation between two values

Andy Farnell padawan12 at obiwannabe.co.uk
Sun Aug 22 21:37:41 CEST 2010

Not sure if I read you right Matteo, but the thing
that popped into my head was some kind of chaotic map
like Lorenz.

On Sun, 22 Aug 2010 21:17:38 +0200
Matteo Sisti Sette <matteosistisette at gmail.com> wrote:

> Hi,
> In my patches (especially in visual ones) I often need some value to 
> randomly "oscillate", or change smoothly, between two extremes, at 
> regular intervals (e.g. change every frame).
> For this purpose I often use filtered noise: [random] followed by a 
> filter of the kind
> y[n]=a*y[n-1]+(1-a)*x[n]
> with 0<a<1
> This is fine when I don't need to have a very precise control over the 
> range and especially when it doesn't have to be controlled dinamically, 
> so I just adjust the "smoothness" and compensate the gain by trial and 
> error.
> But when I need to easily control the minimum and maximum and have a 
> parameter that controls "smoothness" in a natural way, I am not very 
> satisfied with this approach.
> Another technique I use is to have a random increment (which can be 
> positive or negative) added to the current value; then I can force it to 
> "bounce" when it reaches either extreme. Same as above: it works but is 
> often unsatisfying.
> What do you usually use in these situations? I'd prefer a roughly 
> uniform distribution of the final result over a gaussian one, or at 
> least one that would have a minimum and a maximum without clipping (the 
> problem with a gaussian is that you either get a peak in probability of 
> the extreme values, or in order to avoid them, you get very low density 
> for any value near them)....
> I know this is not a well-defined problem, that there are hundreds of 
> answers with advantages and disadvantages depending on the application; 
> but I guess many of you have often needed something similar and I'd like 
> to hear what are your favourite solutions.
> thanks
> m.
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Andy Farnell <padawan12 at obiwannabe.co.uk>

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