In addition to the above, there are several more packages for creating more serious applications working with sound. I will list only a few:

FFTrealKOL - adaptation for KOL of one of the fastest implementations of the fast Fourier transform, author Thaddy de Koning (Netherlands);

Kol32Audio- a package for professional work with sound, including the creation of special effects. Surely useful if you want to create an editor for sound files. The author is the same;

MultiWave- contains an object for simultaneous playback of several dozen audio streams in WAV format. Mixing is done programmatically, the sound is reproduced using DirectSound.

KOLMidi- package for working with MIDI by Thaddy de Koning. There is a demo of KOLMidiTest (in a separate archive).