[music-dsp] Filter Envelopes in Polyphonic VA synths

[eli+ at gs211.sp.cs.cmu.edu]

Nick D wrote:
> Im currently updating every 256 samples on the filter and oscillator
> frequency, and really the quality is ok as far as i can tell. sure,
> it limits your modulation rate before quality does suffer, but what
> do people think? can anyone *really* say it sounds worse?

I'm lazy, got any stress-test examples to listen to?

I do like to use audio-rate filter modulation, so I feel compelled to
build versions of the filter with audio-rate and with control-rate
frequency inputs.  In fact I like to audio-modulate a lot of things.  
In Aura, we used a giant awk script to take inner-loop code from a
unit-generator description, and generate all of the useful rate
combinations.  (Rate choices for each input actually included audio,
interpolated control, stepped control, and updated-by-event.)

(name   SVFilter)
(header {
    #include "ugutil.h"
    #include "defines.h"
})

(args   (a in, abc hz, abc qrecip)  (a lo, a bp, a hi)
        (b in,  bc hz,  bc qrecip)  (b lo, b bp, b hi)
)

(var    (ffloat F1)
        (ffloat vlo = 0.0)
        (ffloat vbp = 0.0)
        (ffloat vhi = 0.0)
)

(depend (hz F1  { 2.0 * fast_sine(Pi*hz/SR(in)) }))

(per-sample {
   lo = vlo += F1*vbp;
   hi = vhi = in - vlo - vbp*qrecip;
   bp = vbp += F1*vhi;
})

-- 
     Eli Brandt  |  eli+ at cs.cmu.edu  |  http://www.cs.cmu.edu/~eli/

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