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I am using a software based synth program and have the option to add a Parametric EQ 'pedal' as an effect before console/mixing desk. This Parametric EQ pedal has 3 knobs: | FREQ | GAIN | BANDWIDTH or Q |: I understand the properties of each of these but what I cannot factor for the life of me is specifically to do with the VALUES given in the | BANDWIDTH or Q | area... I need to know the 'Area Of Effect' or how wide the Q is relative to what specific frequencies it is effecting but the values themselves are just numbers: ranging from 0.10 advancing in increments of 0.01 to a maximum of 12.00 Obviously this would change with the amount of GAIN applied but assuming 0 (zero) GAIN is there an equation to solve this? If it helps in your answer assume A-440Hz and the lowest and highest frequencies effected by a BANDWIDTH or Q value of 6.00 and 12.00 Thanks

Shane Ansell
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Bandwidth = Center Frequency / Quality Factor

See the Wikipedia article on Equalization

This means that the higher the Q, the more narrow the boost or cut, and vice-versa.

For your example, with a center at 440 Hz and a Q of 6, the bandwidth would be 73.33 Hz, shrinking to 36.66 Hz for a Q of 12. For context, the G# below A 440 is appoximately 415 Hz, the A# above it is approximately 466 Hz, so the frequency difference between those two notes is wider than the bandwidth of a filter of Q 12 with a center freqeuncy of 440 Hz.

On a personal note, I never use a calculator when I do EQ, I just use my ears.

Todd Wilcox
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  • In this instance it is vice versa... the smaller value of Q gives less bandwidth (0.10<12.00) the particular reason I ask is to avoid bleed into A# and G#. Specifically, for fabricating the most realistic piano sound I can from a synth. I understand all the parameters involved and just how hard this is but I have done ALOT of work to this end... it's just this particular device/plugin works better than a graphic/visual EQ Excellent answer though, I'll be able to solve it from here using the numbers you've given I guess I just needed a little 'scope' or light on the issue. – Shane Ansell Jun 25 '15 at 18:49
  • If the smaller "Q" is giving less bandwidth, then the numbers do not represent the actual quality factor that the letter "Q" normally indicates. – Todd Wilcox Jun 25 '15 at 18:53