Audibility of Small Distortions

[MRC01]

High Q means numerically high, meaning a narrow filter. Q=0.67 is about 2 octaves wide total, 1 on each side. I consider that as low Q. I think of "high Q" as a notch filter, which I would consider Q=2.0 or greater. Medium, anything in between.
Ask 3 other people and you'll get 3 other answers.

 

[lukyjohnson]

Distortion is measured as the ratio of the harmonic level to the level of the fundamental frequency. This is usually expressed as a percentage but sometimes also expressed as a decibel.