Re: Linear phase IIR filter

Jerry Avins said the following on 09/05/2006 20:41:
Oli Filth wrote:

Jani Huhtanen said the following on 09/05/2006 18:48:

Martin Eisenberg wrote:

Clements, Pease -- Causal Linear Phase IIR Digital Filters
http://0xdc.com/paper.pdf

Intresting paper, thanks. Altough, in the paper the anti-symmetric
case for
linear-phase filters seems to be ignored.

Strictly speaking, anti-symmetric FIR filters aren't phase-linear.
Phase-linear means that:

phi(w) = k.w

(where k is some real constant), as it is for a symmetric FIR.
However, for an anti-symmetric FIR:

phi(w) = k.w + pi/2

This is an affine equation rather than a linear equation, hence these
may be called "affine-phase" filters.

A plot of phase vs. frequency is a straight line. That's linear enough
for me. :-) y = ax + b is generally called a linear (as opposed to
quadratic) equation.


Yes, you're right :). I guess it depends which meaning of "linear" you're using. I suppose I should have said "linear transform" rather than "linear equation". What I meant was, y = ax + b isn't linear in the sense that it doesn't obey superposition or homogeneity...


--
Oli
.

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