# Deciding an EQ's Center Frequencies

I am currently making a relatively simple EQ of a music app, for which we decide to have 5 bands. Other than that, we want to have a bass boost knob, which, as I view it, is just another Peak EQ filter — so a 6 band EQ.

• Are there any standards on what a 5(or 6) band EQ's frequencies should be?
• What should the bass boost's frequency be?

Also, we are making only one Q knob to control the Q for all bands, simply because there isn't any space left for more knobs to be added, but we still want to provide this functionality.

• Is this a good practice/design?
• If not, is it at least acceptable or useful?
• Usually you see octave scale used with constant Q 6-band Peaking EQ starting from 100Hz (... 3.2kHz) but, I quess that's not what you would prefer. You could use EqualizerAPO (Windows) for to find those best center frequencies and Q range for your design. sourceforge.net/projects/equalizerapo . – Juha P Dec 16 '18 at 8:11
• Some useful reading - mdpi.com/2076-3417/6/5/129/htm – Juha P Dec 16 '18 at 15:37
• This might also be of interest. – applesoup Dec 16 '18 at 19:23
• Also, as an alternative to a peak filter, a bass boost may also be implemented via a shelving filter. – applesoup Dec 16 '18 at 19:25
• True, is a LSHV a more common and better practice for a bass boost? If it is I think I'll opt for it. @applesoup – Nicholas Dec 17 '18 at 0:36

## 1 Answer

The audible range is about 10 octaves, and usually the center frequencies of a graphic equalizer would be distributed equally spaced on a log scale to cover that range. Common equalizers have either $$30$$ bands (with $$1/3$$ octave filters) or $$10$$ bands (with $$1$$ octave filters).

If you want $$5$$ bands, you could choose filters that cover approximately $$2$$ octaves. The five center frequencies would then be something like

$$\begin{matrix} 30\,\text{Hz} & 125\,\text{Hz} & 500\,\text{Hz} &2\,\text{kHz} &8\,\text{kHz} \end{matrix}$$

If you have an equalizer like that I'm not sure if an additional bass boost button makes much sense. If you want $$6$$ frequencies, just divide the $$10$$ octaves into $$6$$ equally spaced bands (on a log scale).

• Got it. I'm getting 16-16KHz for the ten octaves (C0-C10), but I know the human audible range is 20-20K. Sounds between 16K-20K is very sharp and not really found in music because its sharpness and may even be considered a noise, so no need to have a band in between 16K-20K. Am I right? – Nicholas Dec 17 '18 at 0:35
• @Edward: It doesn't matter so much if you take 16kHz or 20kHz as upper limit of the audible range. If you use the range 20Hz-20kHz for your equalizer and you define 5 center frequencies in the way I did in my answer you end up with (approx.): 40,160,625,2500,10000 Hz – Matt L. Dec 18 '18 at 13:29