Re: [Ardour-users] Re: good quality reverb - brutefir!

From: Ross Vandegrift (ross_at_willow.seitz.com)
Date: 11/25/03 00:07 EST


From: Ross Vandegrift <ross@willow.seitz.com>
Subject: Re: [Ardour-users] Re: good quality reverb - brutefir!
Message-ID: <20031125050716.GA10500@willow.seitz.com>
Date: Tue, 25 Nov 2003 00:07:16 -0500

On Sun, Nov 23, 2003 at 01:36:54PM +0100, Piotr Sawicki wrote:
> BruteFIR is very interesting, but its documentation is not sufficient to 
> know how to
> convolve filters that use impulse responses.

I spoke last week to my EE friend and he explained this to me.  It's
staggeringly easy.

To apply any filter to any arbitrary signal, aparantly, all you need to
do is take a signal with the filter already applied, and convolve it
with your target signal.  He assured me it really is that simple -
hopefully he wasn't oversimplifying it.

Properties of the original signal can aparantly make this better - a
delta function makes the best signal to convolve your dry signal with.
Unfortuantely, producing a delta function is just a touch impossible in
the real world.

So while I don't know the particulars of how this applies to audio, the
theory seems to indicate it'd be pretty simple.

> >The biggest problem being the lack of impulses. If there where a library 
> >of free impulses I could easily envision bruteFIR becoming a 
> >"killer-application". 

I also began thinking about this after the discussion.  If things stay
about as simple as my EE friend says they are, then we could perhaps
produce some audio files that are "close enough" to a delta function to
give good results.  People could then play them back in a room they
liked and record with a laptop or something.  Bada-bing - instant
impulses.

I'm not sure what kinda of signals people are using for producing these
impulses - I'm guessing it's something really short and frickin' loud...

-- 
Ross Vandegrift
ross@willow.seitz.com

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