## Allpass Examples

- The simplest allpass filter is a unit-modulus gain
- A lossless FIR filter can consist only of a single nonzero tap:
- The transfer function of every finite-order, causal,
lossless IIR digital filter (recursive allpass filter) can be written
as

We may think of as the

*flip*of . For example, if , we have . Thus, is obtained from by simply reversing the order of the coefficients and conjugating them when they are complex. - For analog filters, the general finite-order allpass
transfer function is

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