Robert Keller – Feedback using a phase vocoder

Hi, for my feedback with found systems assignment, I used a phase vocoder that I improved (initially from http://sethares.engr.wisc.edu/vocoders/matlabphasevocoder.html). A phase vocoder is essentially a system that slows down or speeds up audio without altering the pitch of the audio. Designing an industry standard phase vocoder is rather difficult, and the implementation below is not without it’s shortcomings. Namely, the process of speeding down audio using the vocoder below introduces a “phasey” aspect to the resulting audio. The phasey artifacts introduced by the vocoder are initially passable, but if one were to say, slow the initial audio down by a factor of 2, then speed the audio up by a factor of 2, and then repeat the process 20+ times, one would drastically alter the original quality of the audio. The final result is incredibly phasey. The initial piece of audio I used was from the song “Message in a Bottle” by the Police. Below is the resulting audio and code from Matlab.

Here is the script I used to generate the audio:

Original Audio:

Audio passed through phase vocoder once:

Audio passed through twice:

Audio passed through three times:

Audio passed through nine times:

Audio passed through fifteen times:

Audio passed through twenty times:

Audio passed through thirty times: