The "Q" factor is sort of like the range around the center frequency that gets adjusted. As you adjust the level of a frequency you are not just adjusting that exact frequency you are adjusting it and the frequencies around it. The "Q" will adjust how much around that center frequency is adjusted. I believe a high Q is very tight around the center frequency, where as, a low Q will adjust many frequencies around it.

Thats the layman definition. The techie definition would also state that the Q is adjusted by moving the poles in the z-plane of your filter.

Alex Lear