# Q-factor and Frequency Ranges for EQ

I'm doing a bit of research into some audio graphic equalizers and the following questions have come to mind.

1. Typically, what is the Q-factor for a standard audio graphic EQ/band? For example, if one slider is labelled 800Hz, what range of frequencies will that filter pass (let's say the cutoff is the cutoff frequency)?

2. How much overlap is there between filters/bands? For example, does one simply match the high end of the bandwidth for one filter/band, with the low end of the bandwidth of the next filter/band (i.e. matching cutoff frequencies)?

I believe the standard is 1/3 octave, or a Q of about 4.3.

For a thorough discussion of Q and ripple see https://www.ranecommercial.com/legacy/note101.html

One octave is a doubling of frequency; therefore a bandpass filter with passband boundary frequencies f1 and f2 of, say, 100 Hz and 200 Hz respectively, is said to be one octave wide. One-third octave is a 26% increase in frequency (21/3 = 1.26); therefore, boundary frequencies of 100 Hz and 126 Hz respectively would be 1/3-octave wide.

and

The Quality Factor, or "Q", of a filter is a close relative to bandwidth. It is defined to be the center frequency divided by the bandwidth in Hertz. For example, a filter centered at 1000 Hz that is 1/3-octave wide has -3dB frequencies located at 891 Hz and 1123 Hz respectively, yielding a bandwidth of 232 Hz. Q, therefore, is 1000 Hz divided by 232 Hz, or 4.31.

To calculate Q from bandwidth, see http://www.sengpielaudio.com/calculator-bandwidth.htm

In audio more than Q factor you talk in dB/octave of attenuation. Typically they are 12dB/oct bandpass filters.

As for the spacing you often use 3 bands for each octave so there is quite overlap.

High-end or lower range equipment will have of couse different characteristics.