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Making and using all-pass filters

Figure 8.33: All-pass filters. (a). making an all-pass filter from elementary filters; b. using four all-pass filters to build a phaser.
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Patch H14.all.pass.pd(Figure 8.33 part a) shows how to make an all-pass filter out of elementary filters, in this case a non-recirculating filter, second form (rzero_rev~) and a recirculating filter (rpole~). The coefficient, ranging from -1 to 1, is controlled in hundredths.

Patch H15.phaser.pd(part b of the figure) shows how to use four all-pass filters to make a classic phaser. The phaser works by summing the input signal with a phase-altered version of it, making interference effects. The amount of phase change is varied in time by varying the (shared) coefficient of the all-pass filters. The overall effect is somewhat similar to a flanger (time-varying comb filter) but the phaser not impose a pitch as the comb filter does.


next up previous contents index
Next: Exercises Up: Examples Previous: Using elementary filters directly:   Contents   Index
Miller Puckette 2005-02-21