Tutorials and Topics - Peabody Computer Music

Tutorial 31Processing:Comb filtercontinuous sound at any amplitude and frequency by sending numbers from thepitch and velocity number box objects (first velocity, then pitch) into the inlets of the pPulse_Wave subpatch.Varying parameters to the filterAs illustrated in this patch, it’s usually best to change the parameters of a filter by using agradually changing signal instead of making an abrupt change with single number. Soparameter changes made to the “Adjusted By Hand” comb~ object are sent first to a line~object for interpolation over a time of 25 ms.The “Modulated” comb~ object has its delay time varied at low frequency according to theshape of the band-limited pulse wave (just because it’s a more interesting shape than asimple sinusoid). The modulation could actually be done by a varying signal of any shape.You can vary the rate of this modulation using the mod wheel of your synth (or just bydragging on the number box). The gain of the x and y delays (the two rightmost inlets) ismodulated by a sine wave ranging between 0.01 and 0.99 (for the feedback gain) and acosine wave ranging from 0.01 to 0.49 (for the feedforward gain). As the amplitude of oneincreases, the other decreases.• Experimenting with different combinations of parameter values may give you ideasfor other types of modulation you might want to design in your own patches.SummaryThe comb~ object allows you to use very short feedback delay times to comb filter a signal.A comb filter creates frequency-dependent increases and decreases of amplitude in thesignal that passes through it, at regularly spaced (i.e., harmonically related) frequencyintervals. The frequency interval is determined by the inverse of the delay time. The combfilter is particularly effective when the delay time (and thus the frequency interval)changes over time, emphasizing different frequency regions in the filtered signal.The user interface object gain~ is useful for scaling the amplitude of a signal according toa specific logarithmic or exponential curve. Changes in amplitude caused by gain~ takeplace gradually over a certain time (20 ms by default), so that there are no unwantedsudden discontinuities in the output signal.See Alsocomb~gain~Comb filterExponential scaling volume slider240