Four channel system used in audio to try and give the listener the effect of a 360 degree sound field.

Quantization (Quantisation)
In Midi, quantization is the process where midi notes are moved in the time domain. A Midi part will be divided into subsections (e.g. quarter notes, or sixteenth notes). The Midi notes are then moved to the time of the closest subsection.

Often quantization is used to correct timing errors as played by a performer or to change the feel of a Midi part.

Quarter Power Points (Q)
These are the points on an audio response curve of a bandpass filter that define the Bandwidth of the filter. Commonly reffered to as the ‘Q’ of the filter. Each point defines the frequency at which the amplitude of the bandpass response results in a signal power that is 1/4 of the power of that at the peak or central frequency.

All I know is, for every note, there is another note that melts it. I just hear a sound coming into my head and hope to catch it with my hands.”
Errol Garner