Re: IIR v FIR

Randy Yates <yates@xxxxxxxx> writes:

Dirk Bruere at NeoPax <dirk.bruere@xxxxxxxxx> writes:

Are there any benefits to using FIR filters compared to IIR eg
Butterworth, in digital crossovers?
Anyone know how they sound in comparison?

You could almost make a career out of answering that question.

First of all, note that there is no such thing as a Butterworth
digital filter. There are techniques for approximately analog
Butterworth filters using digital filters, but they're not really
Butterworth digital filters.

There are distinct numerical advantages in FIR filters and
those could translate to audible advantages. The most obvious
ones are that they are unconditionally stable and never have
limit cycles. On the other hand, FIR filters require more
computation than IIR filters, and so if you're constrained
in processor speed you could very well end up with a better
achievable IIR filter than achievable FIR filter.

I forgot to add a couple of more points.

Another potential advantage of FIR filters is that they can easily be
made to be linear-phase. You can also with IIRs, but you have to play
tricks.

However, some have said that linear-phase filters don't sound good, so
it may be that IIRs which approximate analog filters like Butterworth,
Chebychev, etc., actually sound better.

Finally, it is possible to combine the potentially good sound of an
analog filter (e.g., Butterworth) with an FIR filter using the FDLS
filter design method [berchin].


For some references, see for example [mitra] and [proakis].

--Randy

@BOOK{mitra,
title = "{Digital Signal Processing: A Computer-Based Approach}",
author = "Sanjit~K.~Mitra",
publisher = "McGraw-Hill",
edition = "second",
year = "2001"}
@BOOK{proakis,
title = "{Digital Signal Processing: Principles, Algorithms, and Applications}",
author = "John~G.~Proakis and Dimitris~G.~Manolakis",
publisher = "Prentice Hall",
edition = "third",
year = "1996"}

@article{berchin,
title = "{Precise Filter Design}",
author = "Greg Berchin",
journal = "IEEE Signal Processing Magazine",
month = "January",
year = "2007"}
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