Octaverter™ is short for Octave Inverter. It's a twenty-first-century algorithm inspired by 1930s voice scrambling technology that turns audio upside down—making melodies go up where they originally went down, turning timbres on the heads, and yet keeping recordings recognizable through it all in ways that verge on the uncanny.

You can read about how it works here. Or you can just listen to some examples of what it can do:

Octaverter is based on well-established principles of frequency inversion, demonstrated in their basic form here on a 6 kHz audio file of the Beatles' "I Want to Hold Your Hand." By inverting source audio in octave-width bands, however, it's able to produce much more aesthetically worthwhile effects.

Want to try your own hand at octave inversion? I've created a Windows 10 executable from my experimental MATLAB code, and you can download a zipped installer for it here. I haven't tested it beyond my own laptop computer, so if you try it out, please let me know how it goes!

Octaverter screenshot

The input can be a WAV or mp3 file; the output will be a WAV. The "Inversion Settings" panel is where you specify the frequency points at which inversion will take place. If you select "split," you'll choose the frequency at which bands are split, and if you select "invert," you'll choose the unchanged inversion frequency around which other frequncies will flip. The "Ref in Hz" window allows you to establish a base frequency. If you select this and nothing else, the frequency specified will be used as the band-splitting or inversion frequency (depending on which you've picked). Alternatively, you can select a frequency in more musical terms. Under "Tonic," select the tonic of a relevant musical key where A equals "Ref in Hz" (default is A=440). You can then select a desired number of semitones above that, and you can fine-tune your selection further in twentieths of a semitone. If you select "All" from the Tonic dropdown menu, Octaverter will batch-generate twelve WAV files, one for each semitone in the octave starting at "Ref in Hz." If you'd like to do an experimental test-run rather than taking the time to process an entire sound file, select "part" instead of "whole" and specify the number of seconds of the source file you'd like to process (default is fifteen seconds).

UPDATE, July 23, 2017. I've been continuing to tweak my Octaverter program and to experiment with other processing techniques. Here's some more sample audio:

"Octaverter" is a trademark of Patrick Feaster. Contact him here.