New Post: Equalizer issues

Max frequency is half Samplerate (Nyquist criteria).

E.g.:
Samplerate 8000Hz -> FFT -> Frequency range: 0-4000Hz -> Max frequency: 4000Hz
Samplerate 44100Hz -> FFT -> Frequency range: 0-22050Hz -> Max frequency: 22050Hz
Samplerate 48000Hz -> FFT -> Frequency range: 0-24000Hz -> Max frequency: 24000Hz

and so on.

Note, that in reality (my own experience) Min frequency is not exactly at 0Hz, but near to it with ~20-40Hz.