Allpassphase Review

For a allpass (more phase shift and steeper group delay peak), the transfer function becomes:

[ H(z) = \fraca_2 + a_1 z^-1 + z^-21 + a_1 z^-1 + a_2 z^-2 ] allpassphase

The coefficient a is related to cutoff frequency fc and sample rate fs by: For a allpass (more phase shift and steeper

In a perfect, linear-phase system (like a pure digital delay line), all frequencies are delayed by the same amount. The waveform shape remains identical. However, in a (like an allpass filter), different frequencies arrive at different times. in a (like an allpass filter)

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