Assignment 7 is to use three recirculating comb filters to impose pitches on a vocal sample of the words "soft and relaxing" spoken by some bygone radio announcer. A comb filter is just a single delay line whose output is multiplied by a gain less than one and fed back into the input
You can get the vocal sample from the file, "voice.wav" in the Pd distribution. The internal path is pd/doc/sound/voice.wav. If you're on a Macintosh you'll have to "open package contents" on Pd to see this file. The sample contains more than just that phrase; you'll have to play a portion of it using tabread4~ (as we saw when working on samplers) or tabplay~. You might have to envelope the sample player to avoid getting a click at the beginning of the phrase.
Then figure out how many milliseconds are in the periods of the MIDI notes 60, 64, and 67 (the pitches of a simple C major chord, called a triad). You can use mtof to get the frequencies and then divide 1000 by the frequency in Hz. to get milliseconds.
Then use delwrite~ and deread~ to make recirculating delays with each of the three lengths. (If you want the pitches to be exactly right you'll need to use vd~, the variable delay read object, which does 4-point interpolation. But I wasn't that fastidious when I made the example output.)
The comb filters should have recirculation gains close to, but not equal to, 1 to get them to ring at the three pitches. Then add the three outputs together and enjoy. The result should sound like this.
For extra credit, using granular sampling techniques such as shown in patches B13.sampler.overlap.pd or B14.sampler.rockafella.pd from the Pd distribution "audio examples", make the vocal phrase "soft and relaxing" last five seconds or so (instead of slightly under a second as it does in the original sample). Comb filter as before. The result should sound like this.