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Alien Autopsy Via Sample-Rate Reduction

Posted on | January 6, 2011 | 2 Comments

Here’s a cool sound-design trick. If you want to get a vocal-sounding ‘formant filter’ effect out of a synth that only has a normal lowpass filter, you can take advantage of a quirk of sample-rate reduction effects to generate multiple “mirrored” filter sweeps through the wonder of aliasing.

Here’s a sound clip from my machinedrum with a simple sawtooth note and a resonant lowpass filter being modulated down over a quick sweep. It’s played four times, each with increasing amounts of sample-rate reduction applied:

increasing srr

This sample looks like this in a sonogram (I used the Sonogram View plugin that Apple includes with XCode). Horizontal axis is time, vertical is frequency:

Notice that as the aliasing (reflected frequencies) increase with the sample-rate reduction effect, you begin to see multiple copies of the filter sweep. This creates the lovely, complicated “alien voice” sound. Here’s a short MachineDrum loop I was playing around with when I realized what was going on here:


And for the Elektron-heads reading this, here’s the MD sysex for that pattern+kit:

PS: the wikipedia article on aliasing has a good rundown on the details of this phenomenon.


2 Responses to “Alien Autopsy Via Sample-Rate Reduction”

  1. JC
    June 7th, 2011 @ 8:20 pm


    Looking for a fractal synthesizer I found your processing experiment (and your juicy soundcloud!)

    Im trying to extract some synthesis soundscapes , aliens or whatever could be inside from interactive strange attractors in processing too… lets see what happen.

    Greetings from Spain.

  2. google.com
    June 14th, 2014 @ 6:08 am

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