December 14th, 2015

Demo of a range of various sounds from cross-modulating two sine waves.

This is a demonstration of a noise production technique -- this sound is not likely to be particularly useful on its own, though you may find certain sections to be good source material for further processing toward some goal. This is noise produced by cross-modulating two sine wave oscillators, with both frequency and amplitude modulation used, plus a variable delay in the frequency modulation that is varied by a low-pass filtered product of the outputs. This is as opposed to using a white noise (random) source and then modifying its output (especially with filters) -- here, no random noise source is employed. The two oscillators feed the left and right channel, but a certain amount of a composite signal is mixed into both to form a solidifying center -- that center signal is taken from the product of the two and simply filtered with a 9-sample moving average.

During the production of this (rather long) sound, I varied certain parameters, namely the center frequency and the spread of each oscillator's frequency modulation. You can hear the wide range of differences possible. For one section where the pitch is relatively high (still with low-frequency rumble), I tightened the spread of modulation considerably to get a very tonal sound.

I find the result surprising and interesting. It is almost like the kind of "wind noise" or turbulence you get from rushing air across different types of surfaces, reminiscent of aircraft hull noise or tea-kettle singing, but at low frequencies it can be indistinguishable from a infinite number of "rumble" sources.

There are some screen shots that might be of interest (and the actual circuit) at this page in the abox2 google group forum, but I honestly don't know if you need to join the group before you can see that forum discussion.


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