Assignment 6

This assignment is desgned to give you practice in the "waveshaping" technique (also known as "nonlinear distortion") by imitating an example from the Radiohead song, "there, there". Here's the extract from the song. It features a sound about 17 seconds long made using two strings of an electric guitar, playing MIDI pitches 59 and 47 (the lower one comes in a bit later than the higher one). The combined (added) signal is being distorted somehow.

As time passes the lower tone (47) rises slightly so that the combination of the two starts to beat. The speed of beating varies over time reaching perhaps 15 beats per second before dropping again, perhaps all the way to nothing. This can be accomplished by making the lower tone's pitch rise from 27 to about 47.3 (I found that value by ear; it's approximate).

Both tones should probably not be pure sinusoids but rather should have harmonics, probably with lower amplitudes than the fundamental; this could be done either with additive synthesis (maybe 4 oscillators) or by waveshaping. I used waveshaping with a "cos~" object to provide the nonlinearity. I had to experiment for a while with the right amplitude osc~ to use and the right offset to add before reading from teh cos~ object to get a reasonable-sounding tone. You could also use FM with carrier frequency equal to modulating frequency and a fairly low depth ("index of modulation"). One way or another, you should find something that's not too bright but not a pure sinusoid eother.

Then you can add the two tones (choosing appropriate amplitudes) and use either a "clip~" object or yet another "cos~" to distort them together. This again takes experimentation to get a good combination of amplitudes for the two tones and possibly adding yet another offset before distorting the sum.

Here's the result I got. Notice that, because the two tones are distorted together, the beating is not just changes in amplitude but in quality; the whole thing sounds like a single tone with a rapidly changing timbre. (If you don't get them to be distorted together, you don't get the right effect: here's what I got when I (incorrectly) applied the same distortion to the two tones separately.)

Sorry - I couldn't' think if a suitable extra credit challenge for this week (but the homework itself might be harder than before, since it's taken from the real world of music.)