Music 171 assignment 8 (due Mar. 3): polyphonic Karplus-Strong

Assignment 8

This assignmetn is intended to give you practice using delay lines. It's to make a Karplus-Strong synthesis instrument (the simplest possible one would be fine) and put it into a polyphonic arrangement exactly as in assignment 6. Again you want a bank of copies of an abstraction and you can generate random pitches as before (or do something more creative...) See the description of example 6 for more details about how to set up the abstraction bank and generate pitches for it. YOu can reuse most of the work you did there.

Karplus-Strong synthesis just means making a tone by putting a burst (usually of noise but anything short-lasting is fine) into a recirculating delay ("comb filter") tuned to any desired pitch. Presto: you hear the pitch.

To tune the recirculating comb filter you need to set two coefficients: the length of the delay line (just the desired period, in milliseconds, of the tone which you can compute from the pitch) and the recirculation gain (which you can set to somethign very close to 1, say 0.999 or 0.9997.

There should be a control as before setting the number of millliseconds (or 100ths of a second if you prefer) between notes.

The result should sound something like this.

For extra credit, make a duration control, setting the time in milliseconds or hundredts for the instrument to lose "most of" its energy (this is fuzzy; the trick is that the feedback coefficient has to depend in a carefully thought out way on the length of the delay line.