#70 Improve firequalizer

[Muhammad Faiz]

Use cubic_interpolate: make equalizer curve smooth.
Increase delay to 0.027: increase accuracy at low frequency.
Use tukey window: increase accuracy at low frequency.
Use zero_phase to compensate delay.
Use gain_entry at 0 Hz instead at 31.25 Hz (by extrapolation): increase accuracy at low frequency.

[Muhammad Faiz]

Here, the frequency response (using headphone preset).

[Ricardo Villalba]

I've just applied your patch (with some changes) in svn r8756.

[Muhammad Faiz]

Thank's.