Pitch shifter

Example G09.pitchshift.pd (Figure 7.33) shows a realization of the pitch shifter described in Section 7.9. A delay line (defined and written elsewhere in the patch) is read using two vd~ objects. The delay times vary between a minimum delay (provided as the "delay" control) and the minimum plus a window size (the "window" control.)

Figure 7.33: A pitch shifter using two variable taps into a delay line.

The desired pitch shift in half-tones ($h$) is first converted into a transposition factor

$$t = {2 ^ {h/12}} = {e ^ {\log(2)/12 \cdot h}} \approx {e ^ {0.05776 h}}$$

(called "speed change" in the patch). The computation labeled "tape head rotation speed" is the same as the formula for $f$ given on Page . Here the positive interval (seven half-steps) gives rise to a transposition factor greater than one, and therefore to a negative value for $f$.

Once $f$ is calculated, the production of the two phased sawtooth signals and the corresponding envelopes parallels exactly that of the overlapping sample looper (example B10.sampler.overlap.pd, Page ). The minimum delay is added to each of the two sawtooth signals to make delay inputs for the vd~ objects, whose outputs are multiplied by the corresponding envelopes and summed.