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This collection of Pitch Programs for the Tiptop Audio Z-DSP module use a pitch shifting algorithm
much like the earliest digital pitch shifters released. Sounds similar to the Eventide H910,
AMS 15-80 (with Pitch board) and Publison DHM 89 can be achieved. These programs are
intended more for pure effects rather than the complex multiple harmony lines later devices
and plugins became known for producing. Chords from single VCOs can easily be made using
the ‘Interval’ programs on the card though.
Pitch shifting in the Z-DSP uses a technique called ‘rotating tape head’ delay lines named after
pioneering tape based experiments in Germany in the 1960s. The tape heads move at speeds
independent of the tape playback path and two heads are crossfaded to make a continuous
output. Much of Karlheinz Stockhausen’s output of that era heavily (ab)uses the two tape
machine method of changing pitch. Digital memory and processing allows the same method
by manipulating two playback positions in memory and crossfading them using DSP. This is a
fairly primitive process compared to what can be done today using FFTs (phase vocoder) and
Time Compression and Expansion, but there is a certain sound associated with it that is undeniably
classic.
The first 6 programs all use the same basic algorithm for independent processing of the Left
and Right Inputs on the Z-DSP. The algorithm looks like this:
Left In —> Pitch Shifter —> Delay Line —> Left Output —> [Analog Feedback to Left In]
Right In —> Pitch Shifter —> Delay Line —> Right Output —> [Analog Feedback to Right In]
The differences in the programs come from the controls and their ranges to give more access to
certain parameters of the algorithm and make certain effects easier to create.
The delay lines have roughly 500ms of delay on the Left and 250ms on the Right channel. This
gives a nice 2:1 rhythmic effect to the delay.