The audio files

  * beatbox.wav
  * buzzer.wav
  * chimes.wav
  * cow.wav
  * dialup.wav
  * exposure.wav
  * harp.wav
  * piano.wav 
  * scratch.wav
  * silence.wav
  * singer.wav

are taken from a programming assignment developed by Keith Vertanen at Michigan Tech.

https://katie.mtech.edu/classes/archive/f11/csci135/assign/audio/index.php