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Author Topic: FIR Filters  (Read 532 times)

Josh Billings

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FIR Filters
« on: July 25, 2019, 08:16:32 pm »

So I've heard a lot about FIR Filters. Does it make a big difference when EQing a system? If so, what DSPs feature them and is it worth spending the extra $$$?

Josh Billings
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Russell Ault

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Re: FIR Filters
« Reply #1 on: July 25, 2019, 11:29:22 pm »

So I've heard a lot about FIR Filters. Does it make a big difference when EQing a system? If so, what DSPs feature them and is it worth spending the extra $$$?

Basically, FIR filters present no real-world advantages over common IIR filters for the things most end-users are likely to adjust.

FIR speaker processing can make a significant difference in speaker performance, but the measurements to create those filters typically have to be done very carefully (and in anechoic environments) and so almost always have to be done by the manufacturer. D&B's ArrayProcessing is another example of FIR filtering being used to good effect (and presumably MLA and Anya are using it too), but again, these are all manufacturer-driven.

The only place you're likely to see end-user FIR filters being implemented with any regularity is in linear-phase crossovers, but my experience has been that the phase shift caused by IIR low-to-high crossover filters is totally inaudible, and latency and processing required to use FIR subwoofer crossovers is totally unachievable in a live context.

In effect, if your speaker manufacturer is using FIR filtering on their products this is usually a good thing (although not required for high quality; my understanding is that Meyer still uses only IIR filtering on its products), but going out of your way to add FIR filtering to a system that didn't come with it from the factory probably isn't worth it.

-Russ
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Matthias McCready

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Re: FIR Filters
« Reply #2 on: July 26, 2019, 09:09:09 am »


my understanding is that Meyer still uses only IIR filtering on its products


I was at a Meyer training last week and can confirm this, they do not use FIR filtering in the galaxy (their live processing unit). They do use FIR filtering in their Bluehorn system to achieve a flat phase response, however, that also incurs 45ms of delay which can be afforded as that is not intended for a live situation.

To my understanding, FIR will add delay, whether you can afford that is up to you.

In general, however, you will NOT hear phase shift in the context of the live domain, if you are curious try placing an all-pass filter on a speaker. Turn it on and off to see if you can hear it (I cannot). The only place I would be worried about inducing more phase shift is a crossover point or between two systems you are trying to use relative to one another. To the point any normative EQ work (i.e. no pass filters) should introduce a nominal amount of phase shift. If I remember correctly as long as you are in within 50 degrees you will not incur more than 1dB of penalty, which is more than acceptable in the live domain.

In general, the best system tuners I know of use very few EQ filters, generally between 1-4, and they usually have a very wide Q. Be careful not to overdo things. EQ is a blunt force instrument and there are many problems we cannot fix with it.
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Nathan Riddle

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Re: FIR Filters
« Reply #3 on: July 26, 2019, 01:09:34 pm »

https://eclipseaudio.com/fir-filter-guide/

Have you read this recently posted article?
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Re: FIR Filters
« Reply #3 on: July 26, 2019, 01:09:34 pm »


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