Assignment 8 is taken from an idea by Gerhart Eckel from the late 1980s that later became the basis for IRCAM"s audiosculpt program.

The input sound is any metallic percussion instrument with a decently long decay -- here is the bell sample I used.

The assignment is to design a time-varying FFT-based filter that transformas the bell sound by only allowing the partials to enter in one at a time. In my realization, partials closest to 1000 Hz. appear first, followed in gradual succession by lower and higher ones.

To do this, proceed as in I03.resynthesis in the Pd examples. You will probably want to use a larger window than in the example -- I used 2048. Instead of simply reading a table, though, you will want to make an audio signal that is zero outside an interval of bins, and one inside it. Changing the lower and upper limits of the interval changes the bass band of the FFT filter.

This can be done in any number of ways; one would be to generate a counting signal (bang~ into line~ inside the FFT window) and use either expr~ or, more simply, comparators (subtract the minimum bin number, multiply by a huge number like 1e10, and clip~ to between 0 and 1).

Finally, when your fearless TA clicks your 'start' button, have the patch play the bell sample through tthe FFT filter and simultaeously ramp the low frequency bound from 1000 down to 0, and the upper one from 1000 up to 10000 (for example) and enjoy the result.

Here is my sample output.