The resonance of an electronic circuit. “Q” actually refers to quality factor. Q is a measure of the sharpness of a resonant peak. The term Q is often used interchangeably with “bandwidth“. This is not entirely correct. It is more accurate to say that Q determines bandwidth (a subtle but distinct difference). Q is most often used in reference to synthesizer filters (sometimes referred to as resonance) and equalizers, but it also applies to capacitors (a measure of efficiency, the ratio of capacitive reactance to resistance at a high frequency) and speakers (a measure of directivity). In speakers, a Q of 1 means the system sends out energy equally in all directions; a speaker with a Q of 2 radiates in a 180 degree hemisphere; higher Q’s correspond to smaller angles. In EQ circuits Q is defined as the center frequency divided by the half power bandwidth. On a 1/3 octave graphic equalizer, for example, the half power point at 1 kHz is 232 Hz wide. The Q is thus 1000/232 or 4.31.