Tone control 3 bands

[Jamesmeister]

So i've found some schematic diagrams having 3 bands (treble,bass,mid) but i can't find any site showing equation on solving cut off frequencies on the 3 bands. i can only find the computation for treble and bass on james-baxandall circuit. we are given specifications(cutoff frequencies and cutboost) that we should meet to design the 3 band tone control circuit.

*credit to the owner of the picture

 

[tinitus]

its commonly called 'tone stack'

 

[mickeymoose]

Here is some of the math behind the circuit: Audio Tone Controls
The mid-band control parts values are established empirically as the math is complex and response is affected by the other 2 controls.
A good start is with C5 similar to C3 and C4 similar to C6 with C5 = 5x C4