Allpassphase -

The coefficient a is related to cutoff frequency fc and sample rate fs by:

[ H(z) = \fraca + z^-11 + a z^-1 ]

Consider a transient sound—a sharp click or a snare drum hit. This transient is composed of a wide spectrum of frequencies. If an allpass filter shifts the phase of the high frequencies relative to the low frequencies, those frequency components no longer align perfectly in time. The result? The peak amplitude of the transient is reduced, the waveform becomes asymmetrical, and the "punch" is softened—even though the frequency spectrum (the EQ) looks identical. allpassphase