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Old 30th March 2007, 08:42 AM   #1
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Default Audio filtering with brutefir

Hi folks.

I'd like to stress a discussion about digital filtering by using brutefir , your experiences with it, the applications you use it for and the way you handle it.
I am about to get myself into that area. I hope I can contribute better to it later on.

This thread I regard as a spin-off of the Linux Audio Thread
and PC The Perfect Source I started up earlier.

I see it as a next step to above discussions. I managed to get the basics IMO well done and don't see much of (sound)-improvement potential on the PC&OS&PLAYER side.

Now I got to the stage where I would like to enter the PC based DSP filter arena.

After some research it seems to me that brutefir should be
it. At least I'll try it.

brutefir could be used as digital

a. volumecontrol
b. dithering filter
c. crossover
d. parametric equalizer
(e. convolution engine - room response equalization) I leave that out for the time being. I expect to much sound degradation by manipulating the whole frequency response.
f. asf

The options and performance are IMO limited to the PC performance only. The filters which can be generated I'd regard much superior over any classical analog filters. I could drop e.g. my Behringer DCX2496 for my subs and my analog crossover filters. The whole filtering would be done in the digital domain - right at the start.
The associated losses should be much less than doing the filtering further down the stream with numerous conversions in between.

IMO there are plenty of reasons for me to start this (DIY) journey.

The filter generation seems to be the most challenging task though. Especially if you are lacking DSP filter theory.
However, there are nice tools such as DRC on http://drc-fir.sourceforge.net/ or www.acourate.com (quite expensive though) available to make filter design easier. (You might want to read this acourate whitepaper )

I had the feeling that brutefir is not really well documented.
One has to search a lot for examples to understand how it really works. ( I still didn't manage very well - perhaps due to my lack of knowledge within this area at his stage.)

My first step will be a very basic setup to see how I can establish just a simple 32bit float volume control and a dithering filter.
(On a first glance after spending two hours on it -- I didn't really figure it out how it works- Anybody around who might help out here? )

Finally the outlook: In the best case just a multichannel soundcard/DAC and a Multichannel AMP would be needed to get a great working system done.
This will save a lot of time and money on good quality parts for
filters, (digital) external crossovers pre-amps and so forth.
And in the end - I hope - it will most probably generate a much better sound then before -- at lowest invest!

I'd really appreciate your comments, opinions and experiences.

Cheers
Klaus
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Old 16th November 2007, 09:40 AM   #2
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Default Still alive?

Hi Klaus,

are you still in the arena of PC-DSPs?
I could offer some expierence with acourate and how I got it going.

Cheers,
Thomas
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Old 16th November 2007, 11:31 AM   #3
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Default Re: Still alive?

Quote:
Originally posted by threefff
Hi Klaus,

are you still in the arena of PC-DSPs?
I could offer some expierence with acourate and how I got it going.

Cheers,
Thomas
Thomas.

Of course I am.
There is IMO no way around it.

Perhaps you read my recent post, related to the Uli Brueggemann full brutefir digital filtered chain in the Linux Audio thread.
I met him 2 weeks ago on the DIY fair in Gelsenkirchen.
Very impressive -- his chain.

I just finished up my 2nd DAC.

Now I need to do the system and in-room measurements to be able to do the filter generation.
Unfortunately I am lacking high quality measurement/recording equipment.
I got a Behringer ECM 8000 and a rather poor soundcard for recording. However - for the beginning that could be sufficiant.

I wrote a "Linux Wiki" here at DIY-Audio. I added a brutefir section. Perhaps we should add a "filter" section.

Just drop me a mail. We could take further details offline for the time being.

Cheers
\Klaus
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