
COMB FILTER 2
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Comb filter with separate Feedback and Feed-forward lines, each one with its multiplier (gain), plus optional multiplier for the comb part:

      +-->---[FWD GAIN]--------->----------+
      |                                    |
 -->--+-+->--[DELAY D]-->--+--[COMB GAIN]--+-->--
        |                  |
        +-<--[FB GAIN]--<--+


This filter can be used both as feedback comb filter, feed-forward comb filter or even as an all-pass filter, by suitable choice of the multipliers.

Feedback, feed-forward and comb gain pins accept values in [-1, 1].
Delay (max 8192 samples) can be specified either in samples or in Hz (frequency of the resulting wave length, Hz = rate / samples).
Reading from delay buffer is performed using all-pass shifting, to ensure a flat spectrum response for all fractional delay values.

Gain pins are provided as non-modulable float pins for efficiency, and because modulating them would have little purpose.
Delay pin can be freely modulated instead, if needed.

Feedback comb filtering has the effect of resonating all harmonic peaks of the specified frequency, including harmonic 0 (DC), the more so the closer feedback factor is to unity; with a negative feedback factor instead, the same harmonic series is shifted to the left by Hz/2.

Conversely, feed-forward comb filtering has the effect of creating harmonic 'notches' shifted by Hz/2; with a negative feed-forward factor instead, the same series of harmonic notches is not shifted and includes DC.

A combination of the two may result in all-pass filtering, by suitable choice of the scalers (e.g. feedback gain = g, feed-forward gain = -g, comb gain = 1-g^2).


NOTE: static updates are not supported, since it would make no sense with such a module. When input becomes static it will be muted, no matter if its static value is not zero, and the module will go to sleep once any ringing tail has extinguished.

NOTE: this module is not suitable for high quality delay-based synthesis (Karplus-Strong). Please rather refer to the Digital Waveguide.

  