[sdiy] IR Reverb

Bruno Afonso bafonso at gmail.com
Thu Feb 15 16:09:08 CET 2018


Another way to think of IRs is as a way to capture the response of whatever
thing that processes/affects sound at a given position. A reverb could be
thought of a room processing a sound the same way a guitar pedal such as
delay or distortion or a Woden case.  The reason IRs are not the end all be
all is that a lot of interesting things are not time invariant or linear.

There are indeed ways to speed up convolution, some of which are patented.

On Thu, Feb 15, 2018, 05:17 Richie Burnett, <rburnett at richieburnett.co.uk>
wrote:

> An impulse response takes energy from one point in time and moves it
> around in time. This "redistributing" of energy in time is actually the
> same as filtering. It just might not intuitively feel like it unless you
> were told it in a DSP class or something.
>
> If you have a very long delay then it is obvious that it will produce
> seperate audible echos. However we know that short delays of only a few
> microseconds or milliseconds produce something we call comb filtering,
> (think flanger). So depending on the amount of delay you might intuitively
> think of either echoes or filtering.
>
> A sufficiently long impulse response captures it all, and in fact there is
> really no distinction. If you do something to a signal in the time domain
> it will have implications for its frequency content, and if you do things
> to it in the frequency domain with a filter it alters the waveform in the
> time domain.
>
> In fact an impulse response is all you need to fully characterise a
> system, provided that it is linear and time-invariant. In other words, you
> can fully replicate all of the characteristics of a room's response by
> capturing and applying it's impulse response, as long as the room doesn't
> distort sound, and as long as the sound source, walls and listener are
> static, and there aren't any air currents in the room.
>
> -Richie,
>
>
> Sent from my Xperia SP on O2
>
> ---- Tim Ressel wrote ----
>
> >(note: laughter is understandable and probably mandatory)
> >
> >So I just did a cannonball into the murky waters of impulse response
> >reverb. My tenuous grasp of DSP coupled with my sketchy math skills is
> >making this, well, interesting. So far I have acquainted myself with
> >linear convolution, which looks suspiciously like an FIR. Since it says
> >"impulse response" on the box, that seemed to make sense. But then I
> >stepped back and tried to imagine a reverb system as I understand it and
> >got confused.
> >
> >Reverbs have two things going on: time delay and filtering. The time
> >component gives the reverb time and overall thickness of the reverb,
> >while the filtering can make the effect warmer or colder (yes,
> >oversimplified). So I am guessing the impulse response is a room
> >characterization used to color a reverb. However that seems incomplete.
> >Unless the impulse response is really long or is sets of impulse
> >responses over time.
> >
> >I suspect that gurgling sound is me in over my head.
> >
> >--
> >--Tim Ressel
> >Circuit Abbey
> >timr at circuitabbey.com
> >
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