Allpass1 class overview

Allpass1 is a simple filter that transmits all frequencies without affecting their amplitudes; however, the allpass filter delays frequencies by different amounts according to the filter gain as can be seen in the group delay plot for this allpass filter. Note that if the gain g of the filter is 0, then the delay amount for all frequencies is 1 sample. Here is a flowgraph view of the first-order allpass filter:
 

[Allpass1 flowgraph]
The pole-zero diagram for the allpass filter below show the general placement of poles and zeros for an allpass filter. Poles lie within the unit circle and zeros are placed at the conjugate angle of the pole with an inverse distance from the origin. For the Allpass1 filter, g can only be real, so the pole-zero pair can only be found on the real axis. The magnitude of w along |z| = 1 (the dashed circle) is constant.
 
[Pole-Zero Plot for Allpass1 filter]

First-Order Allpass Filter Characteristics:


Input/Output parameters for the Allpass1 class

Input index Description Summary
0 input signal Incoming signal to be allpassed.
1 gain A number between -1 and 1 that represents the gain used in the allpass filter.
Output index Description Summary
* output signal the allpassed output signal.