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Reverb early reflections

binaryoblivion
KVRer
 
26 posts since 18 Feb, 2016

Postby binaryoblivion; Sun May 07, 2017 7:50 pm Reverb early reflections

I am conducting research into reverberation, with the goal of building my first reverb plugin. I plan to begin by implementing Dattorro’s figure-of-8 reverb “tank” since it is well documented, but I am uncertain how to implement early reflections.

From what I understand early reflections are commonly implemented as a tapped delay line. Is this a sensible approach, or is this method outdated?

Assuming that a tapped delay line is a sensible way to proceed, is there any preferred number of taps, or delay lengths, to achieve early reflections that sound pleasing? I am familiar with the tap lengths and gain values described by Moorer in “About this reverb business”. Are these values worth considering, or is tuning likely to be needed?

If anyone has any tips about early reflections I am all ears!
Miles1981
KVRian
 
1171 posts since 26 Apr, 2004, from UK

Postby Miles1981; Sun May 07, 2017 10:27 pm Re: Reverb early reflections

I think they are still valid, but values will need to be adapted, as they only work for a given sampling frequency :/
binaryoblivion
KVRer
 
26 posts since 18 Feb, 2016

Postby binaryoblivion; Sun May 07, 2017 10:45 pm Re: Reverb early reflections

I would convert the ms delay values into sample values based on the current sample rate, so no problem there. I am more interested in whether the ms values and general approach is still relevant, and it sounds as if you think they are. Thanks!
Miles1981
KVRian
 
1171 posts since 26 Apr, 2004, from UK

Postby Miles1981; Mon May 08, 2017 1:02 am Re: Reverb early reflections

You have the time, but you also have the amplitude to modify!
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ottohalmen
KVRer
 
6 posts since 19 Jan, 2017, from Helsinki, Finland

Postby ottohalmen; Mon May 08, 2017 2:29 am Re: Reverb early reflections

It depends on what kind of reverb you want to create. :)

You could calculate the ER times with a geometric model (e.g. the image source method) for "physical correctness", or you could go with an abstract model similar to this if your goal is just to have the ERs create the impression of placing instruments further back in the room.

As to the image source method, rectangular rooms are the easiest to work with since the math simplifies to the Pythagorean theorem, but you'll probably want to avoid things like perfectly square rooms. Acoustics websites (e.g. Cardas) tell that golden ratio rooms are preferable for listening, so the same might hold true for artificial room reverb as well.

As to the ping pong delay, I think the original 30ms ping pong is still patented (!), so you might not want to use it unmodified, especially if you plan on commercial distribution.
binaryoblivion
KVRer
 
26 posts since 18 Feb, 2016

Postby binaryoblivion; Mon May 08, 2017 12:23 pm Re: Reverb early reflections

Miles1981 wrote:You have the time, but you also have the amplitude to modify!


Moorer's example includes gain settings for each tap :)
binaryoblivion
KVRer
 
26 posts since 18 Feb, 2016

Postby binaryoblivion; Mon May 08, 2017 1:00 pm Re: Reverb early reflections

ottohalmen wrote:You could calculate the ER times with a geometric model (e.g. the image source method) for "physical correctness", or you could go with an abstract model similar to this if your goal is just to have the ERs create the impression of placing instruments further back in the room.


Thanks. I will see what information I can track down about calculating room acoustics. For my purposes I just need to simulate an idealised rectangular space. I am not concerned with accurately simulating a real environment.

ottohalmen wrote:As to the ping pong delay, I think the original 30ms ping pong is still patented (!), so you might not want to use it unmodified, especially if you plan on commercial distribution.


Don't worry, I have no plans to use a ping pong delay in my reverb!
xoxos
Mr Entertainment
 
12018 posts since 29 Apr, 2002, from i might peeramid

Postby xoxos; Tue May 09, 2017 1:19 pm Re: Reverb early reflections

yes you do :hihi:

there was a fair thread only a few months back in this forum about reverb. i'm only a dabbler but i'll agree with what i read - go fish.. there's no reliable "method" for developing a "quality" reverb algorithm (at least that anyone is going to talk about). too sparse too dense too perfect too modal, dig what you can.

fwiw otherwise i'd have said what otto said - geometric options apart from performance criteria. my experience (..not much) is a little more diverse than some of these folks tho, because i design reverbs for procedural *patching*.
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binaryoblivion
KVRer
 
26 posts since 18 Feb, 2016

Postby binaryoblivion; Wed May 10, 2017 1:43 pm Re: Reverb early reflections

Thanks xoxos. I figured that tuning of the reverb early reflections would be required, which ottohalem and your answers confirm.

Reverb is a daunting topic to research compared to other delay-based audio effects like chorus. At this stage I am planning to implement an existing algorithm, which I know will be less than perfect, but hopefully it will give me a basis from which to experiment and build. And if nothing else, it should give me a better understanding of how reverbs work under the hood!

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