Thursday, October 01, 2009
SHIOITOR's High resonance frequency sweep spectrum
YouTube via d16group. D16 Shiotor posts
"High resonance cutoff frequency sweep. All oscillators turned off. Notice that aliased audible artifacts are due to mpeg compression in this movie not the SHIOITOR itself :)"
4 comments:
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What about the *visible* aliasing artifacts? One can clearly see the upper harmonics bouncing back towards the lower spectrum as the cutoff frequency increases. And those have nothing to do with the video compression.
ReplyDeleteI'd guess those would be present anytime you push a frequency past the human range of hearing, where the sample rate of the analysis begins to fight with the frequency of the waveform.
ReplyDeleteI think I've seen that behavior on analog synths as well. Try recording the sine wave output of a self-osciallating filter at 16/44 as you sweep it all the way up past the threshold.
"What about the *visible* aliasing artifacts?"
ReplyDeleteYou need some amount of transition band, no matter what you do (unless you use infinite filter kernel, which you can't exactly do in real-time). Beyond some point improving things further is just waste of CPU.
Yes, it actually looks clean. Unfortunately, I'm not exactly sure why that would be very special. Maybe ten years ago.
I also want to add, that clean self-oscillation all the way up is actually very easy to get, if you oversample at all (and you should). Because stable self-oscillation relies on saturation, the saturation will somewhat counter whatever feedback gain keeps the self-oscillation alive, and you can control the amount of harmonics by controlling the feedback gain (or equivalent, for filters which are controlled by in other ways).
ReplyDeleteMore interesting would be to see how clean they are when feeding the filter (in self-oscillation) with high-gain saw or pulse or something, at high frequency (say 1kHz or up), such that the input would force the self-oscillation against the saturations. This sort of stuff tends to alias much more.