Reverb designs

Warp69 · Post by **Warp69** » Mon Jun 18, 2001 10:53 pm

Hi,

I use Scope DP mainly for testing different types of reverb algorithms, including time-variant FDN reverberators. So ask away, if you need help

[ This Message was edited by: Warp69 on 2004-03-13 09:41 ]

Obsidian · Post by **Obsidian** » Tue Jun 19, 2001 4:31 am

Just a sanity check... FDN is basically a many-tap delay right or are the taps modulated in some weird way?

Warp69 · Post by **Warp69** » Tue Jun 19, 2001 6:48 am

Hi Guy,

FDN stands for Feedback Delay Networks. FDN can be represented as a parallel tank of taps interconnected via a energy-preserving feedback matrix. This matrix can be modulated in different ways.

Apparently, allmost all reverb plugins for Scope/Pulsar use a Moore/Schroeder algorithm. It's based on a tank of parallel comb filters, which is connected to a tank of cascading allpass filters. This approach have some drawbacks : Tonal coloration of the tail and lack of high echo density - They sound Metallic.

[ This Message was edited by: Warp69 on 2004-03-13 09:42 ]

Neutron · Post by **Neutron** » Tue Jun 19, 2001 9:40 am

Do you know how Quantec do it? i know they do things a bit different.

John Cooper · Post by **John Cooper** » Tue Jun 19, 2001 9:46 am

On 2001-06-19 07:48, Martin Lind wrote:
BTW, how can I include pictures??

just include HTML in your post. in other words you'd write a link like <IMG SRC="link-to-your-picture">

cool discussion btw

-john

[ This Message was edited by: John Cooper on 2001-06-19 10:47 ]

Warp69 · Post by **Warp69** » Tue Jun 19, 2001 10:00 am

Nope, I have never tested a Quantec reverb. But my guess is they use a combination of UFDN (allpass feedback structure) and nested allpass filters...... Hmm I don't know - sorry!!!

[ This Message was edited by: Warp69 on 2004-03-13 09:43 ]

Warp69 · Post by **Warp69** » Tue Jun 19, 2001 11:19 am

Hi,

Here are some pictures explaining the Moore/Schroeder reverb algoritm :

1) The two tanks (Comp filter and Allpass filter)

<IMG SRC="http://maeli.punqtured.dk/Scope/Tanks.jpg">

2) Inside the Comp Filter Tank - as you can see, there are 8 comp filters. This is mono, if you need stereo, you have to add 19-35 to all the delay values in the right channel.

<IMG SRC="http://maeli.punqtured.dk/Scope/Comp Filter Tank.jpg">

3) Inside the Allpass Filter Tank - As above, if you need stereo.

<IMG SRC="http://maeli.punqtured.dk/Scope/Allpass Tank.jpg">

4) And now we are inside the Comp filter.

<IMG SRC="http://maeli.punqtured.dk/Scope/Comp Filter.jpg">

I hope you all understand what I mean, if not - Don't hesitate to ask!!!

[ This Message was edited by: Warp69 on 2004-03-13 09:43 ]

Warp69 · Post by **Warp69** » Tue Jun 19, 2001 12:31 pm

Hhmm,

you can download the pictures from :

http://www.filesanywhere.com
login : Scope
pass : pass

John Cooper · Post by **John Cooper** » Tue Jun 19, 2001 12:50 pm

um, yeah, i should have mentioned that when you do the img src = "link" - that link must be accessible on the internet! (not a link to C:\ on your hard disk!)

btw, you can edit your own posts to fix mistakes (just click on the edit button underneath your post).

-john

EarlyFirst · Post by **EarlyFirst** » Tue Jun 19, 2001 1:15 pm

http://www-ccrma.stanford.edu/~jos/cfdn ... works.html

here's a link for FDN's and waveguides

Great Post Martin,
I would love to talk reverbs with you, my new versions use something similar to this,but at the same time still use the Moore/Shroeder design I buit the feature into the devices ;0)
As well as some cool binaural functions which are working very nicely.

Cheers
Paul
EarlyFirst
http://www.earlyfirst.com

[ This Message was edited by: EarlyFirst on 2001-06-19 14:17 ]

[ This Message was edited by: EarlyFirst on 2001-06-19 14:29 ]

Warp69 · Post by **Warp69** » Tue Jun 19, 2001 2:05 pm

Hi Paul,

I have been working on a Reverb for some time now. Im using UFDN & 12 taps time-variant FDN. Just included early reflection.

Remember to modulate the taps in your reverb. You can use 1st order linear interpolation (or allpass interpolation for better sound quality). And don't be afraid to use things like chorus and compressor in your designs (just look at some Lexicon/TC Electronics hardware reverbs).

You are welcome to email me or just ask me here, if you have any quenstions

Best regards

[ This Message was edited by: Warp69 on 2004-03-13 09:44 ]

Micha · Post by **Micha** » Wed Jun 20, 2001 2:12 am

What a post! Since beginning reverb was THE headache of the platform. PCM91? REALLY?? Dear Martin, I hope you do not plan to use this for exclusive own private use. (Can you imagine the hungry Pulsarians sitting before and reading this post? Screaming for reverb with last effort in their broken voices?) Please let us know when, where and how much. I had a look in the formulas. Puh! Not easy! So Pulsarians, let us smoke+drink a few less and put it into the reverb-savings-account!
Happy pulsaring
Micha

Warp69 · Post by **Warp69** » Thu Jun 21, 2001 10:30 pm

At the moment it's a private project (it's far from finished). The following things are still missing :

* A nice looking user interface
* Different types of early reflections (I only have one)
* Optimization of the algorithms
* Things I can't remember right now

Cheers

[ This Message was edited by: Warp69 on 2004-03-13 09:45 ]

jilhead · Post by **jilhead** » Fri Jun 22, 2001 12:17 pm

Thanks to Martin, I did a search on some key words (Jean-Marc Jot, Moorer, Schroeder) and came up with a whole list of papers and circuit diagrams on reverbs. Here is a quote which seems to capture the essence of a reverb:

Analysis and synthesis of room reverberation based on a.. - Jean-Marc Jot.. (Correct)
.... model Moorer noted the auditive resemblance between a concert hall impulse response and a white noise multiplied by an exponentially decaying envelope, and reported that such a synthetic response can produce, by convolution with anechoic signals, a natural sounding reverberation effect [19]. To obtain a frequency dependent reverberation time, he suggested using a filter bank and summing the subband signals after multiplying them with different exponential envelopes (Fig. 1) Polack [2] developed a time domain model complementing Schroeder s frequency domain model. In this model, a ....

http://citeseer.nj.nec.com/context/209676/0

jilhead · Post by **jilhead** » Sat Jun 23, 2001 3:42 am

Unfortunately for me, and I claim to be no expert, I haven't liked any reverb I've come accross since I heard the top of the line Lexicon at a demo (about 10,000 pounds. My mind doesn't work with figures that big very well, so excuse me if I'm out a couple of thousand). The demonstration team demonstrated the smoothness a reverb added to the sound of a snare drum, while only demonstrated voice through the lower end models. Well the question was begging... what did the drums sound like through the lower end reverb, so I asked if they'd kindly let me hear the drums through the latter: in my mind the answer was, 'why would you want to... it sounds so bad in comparison'.

I hoped that something on the creamware platform might save me from my expectations, but my experience so far is that the platform just isn't capabable of it.

BTW, I don't like the creamware delays or reverbs, they both sound harsh and metallic to me. For some reason metallic reverb kills my creative process. As for that excuse for a chorus! (Anyways, I can't criticise without a little praise... I do love the synths, routability, etc, even they if it did do my head comming to terms with them. I can but forgive).

On the reverb front, the software reverbs in Logic Audio have 'kind of' made up for this, and the sound of sonic timeworks reverbs (software) is 'okay'... not that I can justify a splash on the timeworks stuff yet. In general, the software reverbs fall down in that they sound 'thin' to me. There is something missing from them.

Am I alone, or is there one that perceives as I?

Jilhead

Warp69 · Post by **Warp69** » Sun Jun 24, 2001 3:24 am

Hi Jilhead,

You're not alone - thats why I started this thread. I was hoping we could have a discussion, regarding 'high-end' reverb algorithms.

Cheers
Martin

EarlyFirst · Post by **EarlyFirst** » Sun Jun 24, 2001 4:14 pm

Martin,
one hint when using the PC delays the feedback mdl is not needed.

Cheers
Paul

Warp69 · Post by **Warp69** » Sun Jun 24, 2001 10:40 pm

Hi Paul,

Yeah, I know. But I just thougt that the routing was more clear, when I included the feedback modul

Another hint, when you're working with delay lines, work in 48KHz. A delay of 1000 samples in 44.1KHz is only (1000*44100)/48000 = 918 samples.

Cheers
Martin

EarlyFirst · Post by **EarlyFirst** » Mon Jun 25, 2001 8:58 am

haha cool Martin,
That's what I thought but was making sure.

lately I have been testing at 96k

I got a nice little 96K *ONLY* verb coming PT 96K.
which means it was built tested and ran only at 96K in order for people to take advantage of this samplerate.

Cheers
Paul

Warp69 · Post by **Warp69** » Mon Jun 25, 2001 9:04 am

Hi Paul (please check your PM),

I am using the array modul for the different samplerates, since it's pain in the *** when you are working with interpolations

Cheers
Martin

[ This Message was edited by: Martin Lind on 2001-06-25 10:17 ]