KVR :: Effects » Convolution confuses the h-ll out of me [View Original Topic]
There are 32 posts in this topic.

---

DrGonzo - Thu Feb 23, 2012 9:10 am

---

I just don't get it. Convolution is fine for reverbs - but not for compression, distortion and modulation effects? But wasn't Focusrite Liquid Channels built on convolution? And Nebula.

/C

---

jupiter8 - Thu Feb 23, 2012 9:14 am

---

Focusrite Liquid Channel uses (i believe) dynamic convolution and Nebula Volterra Kernels.

---

Shy - Thu Feb 23, 2012 9:16 am

---

It's not fine for reverbs either as far as I'm concerned.

Here's my favorite commentary about convolution used for reverb, by Michael Carnes (Lexicon reverb designer):
http://www.gearslutz.com/board/4075701-post132.html
http://www.gearslutz.com/board/4075956-post140.html

---

meloco_go - Thu Feb 23, 2012 9:18 am

---

Imagine convolution as sort of "snapshot" of the system. Simple convolution uses only one "snapshot" that does not change with respect to incoming signal properties -- completely different to what, say, a compressor does.
Liquid Mix (dynamic convolution) technology adds another dimension to that: different incoming levels would get different "snapshots".
Nebula is something even more advanced.

---

DrGonzo - Thu Feb 23, 2012 9:34 am

---

Got it. Thanks for clearing it out for me.

/C

---

A.M. Gold - Thu Feb 23, 2012 7:52 pm

---

A bit of a conflict of interest issue with that commentary, I'd say.

I think convo for reverbs can run in parallel with algo and I do this sometimes. I tend to find it a bit dry and unrealistic on its own.

---

valhallasound - Thu Feb 23, 2012 8:53 pm

---

No, Carnes is 100% right. There is no argument. No conflict of interest. Nothing to see here. Move on.



Barry Blesser has written some arguments against convolution reverbs, that are pretty convincing to me. Of course, it is worth noting that Barry Blesser created the algorithmic reverb used in the EMT250 (which was recently recreated by Universal Audio), and also recently patented a new allpass filter design which is now licensed by Lexicon. However, just because he may have a conflict of interest, doesn't mean he is wrong.

Sean Costello

P.S. I, of course, have no conflict of interest, and reside in a realm of pure objectivity and logic.

---

Zaphod (giancarlo) - Thu Feb 23, 2012 9:12 pm

---

not true. Try "theater of life" library for nebula. You can place your instruments accurately and it's *dynamic*

http://www.roomhunters.net/joomla/index.php?option=com_content&view=article&id=48&Itemid=56

---

aciddose - Thu Feb 23, 2012 9:22 pm

---

there isn't a conflict of interest regarding the basic fact he's stating.

the fact that a convolution measured from a single point at a single intensity measures that single point and single intensity only.

an algorithm may produce results that are very good at multiple points and intensities, and you might measure multiple points and intensities from a real space and record them as impulses as well.

never did he say anything except this one fact. it's just stepping in to call "bullshit!" when someone says something that is obviously not wholly true.

if you were to say that an impulse captures a complete space, that simply isn't correct. it captures only one source and one listener position in a fixed configuration within that space.

convolution isn't difficult to understand for those confused. here is an explanation:

step one: take an impulse. this is a series of zeros with a single one in them. 0, 0, 0, 1, 0, 0, 0,
step two: play this impulse through your system and record the result. it could be a filter of any sort with linear response. now you have recorded the effect applied by that filter.

step three: repeat the action of the filter on each impulse you want to apply the filter to. how do we do this?

it's simple. say you have a wave. something like 9, 12, 4, 51, 5. this is the same as 1, 1, 1, 1, 1, only with a different amplitude for each impulse. so we have 1,0,0,0,0,0, 0,1,0,0,0,0 and so on. we can pick out each one of these impulses.

step three explained: replace each impulse (sample) in the signal with the recorded impulse response from the filter scaled to the same amplitude as the original impulse.

so we get (IR * 9), (IR * 12), (IR * 4), etc.

now we could also have measured what we get if our impulse is 1, 5, 10, 25, 50. rather than using 9, we could use 10 at a slightly lower scaled amplitude. (IR10 * 0.9) = approximation of IR9.

i'm not sure what the other method includes, but i can think of many different ways you could measure variations on impulse content (frequency bands for example, or phase) and put those back in place of basic impulses from your signal after it has been filtered to bring out that data... but that all gets way too complicated.

the other methods, they might be something simple instead, i'm not sure.

that's convolution explained though!

---

aciddose - Thu Feb 23, 2012 9:28 pm

---

the difficult thing beyond those simple methods is how to make the impulses of different amplitudes and phases interact as they do in the system they were measured from?

an example of a non-linear system with interaction: we should all have used an envelope follower at some point. we should all know that if you play two notes rather than one, you get a unique interaction of those two notes. the result is not the same as if you had played each note individually into the follower, then mixed the outputs together.

an impulse response measurement is going to be a simple recording of "one note". the real problem is how can we reproduce the effect we get when you play two notes at once?

one way would be to measure every possible combination of impulses. the size of the data would become impossibly large. it would also introduce enormous latency and processing cost.

also: an explanation of non-linear. a better term to use is a system with hysteresis.

http://en.wikipedia.org/wiki/Hysteresis

---

DrGonzo - Thu Feb 23, 2012 11:30 pm

---

Weirdly enough I tend to feel the same. Thinking back - during all my year of making music, I'm not even sure if I've ever used a convolution reverb in an actual production. I always tend to find favourite algos (EOS is my favourite for the last two years) and stick with them. Bought NI Reflektor and haven't used it more than ten minutes or so.

Weird.

---

Zaphod (giancarlo) - Fri Feb 24, 2012 11:31 am

---

acidose, he said a different thing



which is misleading, you could use a simple convolver and choose a different impulse response for each clarinet, so you miminc the exact position in that way. Many ir libraries feature different positions. I remember even free libraries from noisevault.com

About what you are saying



nebula, which is in part based on nonlinear convolution can do that, exactly like liquidchannel does, and I think also a couple of convolvers, for example reverberate from liquidsonics.

And again



is still misleading, both nebula and liquidmix, sintefex and many others can do that. I pointed a library for nebula which features:

1) dynamic harmonic distortion
2) dynamic convolution
3) position of the virtual speakers

and that's better than what maybe even a classic algorithmic reverb does. Nebula is considered based on "convolution".
Again



and that's misleading. In 2009 both reverberate, nebula, liquidchannel, liquidmix, sintefex were released.

---

Shy - Fri Feb 24, 2012 3:18 pm

---

There's no convolver ("dynamic" or not) that provides different responses for instruments that are playing together, nor for their different and/or varying intensities.

Even when applied on a single, "monophonic" instrument, the impulse response of "dynamic convolvers" is hardly "dynamic" compared to a real or algorithmic reverb and also depends on varying and "interpolating" between different static impulse responses and you never get an "accurate" response, just a weird sounding "dynamic snapshot" that isn't in any way more "accurate" than an algorithmic reverb, and I'd say even worse than a single static impulse response.

To get any kind of "randomness" (instead of the exact same impulse response used continuously) in the reverberation, which exists naturally in any reverb and isn't a ridiculous static snapshot, you also have to vary between impulse responses and you can't do that in any way that avoids totally weird results. This may work satisfyingly with some very short millisecond length impulse responses, it doesn't work with reverb. You can argue with that if you want, but I'd say the results and sensibility just speak for themselves.

Calling Michael's comments misleading doesn't give you any credibility at all. He obviously never intended to mislead nor said anything misleading, and coming mainly from the classical music field, he was talking about real people playing real instruments, so playing a single instrument each time in that context is completely out of the question.

---

aciddose - Fri Feb 24, 2012 9:20 pm

---

well, when i read it the result i get is exactly the same.

---

Zaphod (giancarlo) - Sat Feb 25, 2012 6:02 am

---

I'm speaking about an action. That couple of posts are misleading imoho and I explained why I think so. I'm not speaking about who posted it or you. I even wrote something stronger, but since english is not my primary language I fixed it a bit, in order to be sure about the message. I try to explain it better: someone could do something wrong, intentionally or not, it doesn't tell you anything about him. It could be a marketing approach, it could be a mistake. This is the spirit of a discussion, though. Misleading in my poor english means "it leads to confusion".
When you are speaking about me, using the word "credibility" your are moving things to a different level. So I'm out.

---

Shy - Sat Feb 25, 2012 6:30 am

---

Like you, I was referring to the topic itself and not anyone's personality (which I couldn't care less about). You argue that it misleads, I argue that considering your expertise on the matter, the trustworthiness of your argument should not fall short as I think it does, resulting in lack of credibility considering what has been established so far in the field on convolvers used for reverberation. All is subjective and as far as I see it. If you want to consider it "personal", too bad.

---

whyterabbyt - Sat Feb 25, 2012 6:56 am

---

how many reverbs of any kind are there that do?

---

Hink - Sat Feb 25, 2012 7:43 am

---

I'm pretty much thew same way for reverbs (IRs for speaker emulation is a different matter) but for me I go straight to variverb

---

DaveClark - Sat Feb 25, 2012 8:47 am

---

Hi all,

Having worked in convolution for over ten years now, beginning with working through a text on Green's function methods (G. Barton's book) and finding that "convolution reverb" and binaural recording simulations more or less fell into my lap:



I agree 100%. The many claims (not just "one fact") are false and/or extremely misleading, depending upon how you interpret terms such as "point" and "capture the space." Those two posts cited above comprise the most inaccurate depiction of convolution (and acoustics) that I have ever seen, and I've seen quite a few.

Regards,
Dave Clark

PS: Recommendations for reading/studying:

Gabriel Barton. Elements of Green's Functions and Propagation: Potentials, Diffusion, and Waves. Oxford, 1989. Reprinted 1991.

Philip M. Morse and K. Uno Ingard. Theoretical Acoustics. Princeton University Press, 1986. Originally published by McGraw-Hill, 1968.

Allan D. Pierce. Acoustics: An Introduction to Physcial Principles and Applications. AIP, 1989. Originally published by McGraw-Hill, 1981.

V. John Mathews and Giovanni L. Sicuranza. Polynomial Signal Processing. Wiley, 2000. Contains sections on multidimensional discrete FFT representations of truncated Volterra series expansions.

---

Hink - Sat Feb 25, 2012 10:50 am

---

Dave, please understand my post wasn't about any of that...I simply was agreeing that I have never used a convo reverb in a song. That's only because I find variverb to be what is most intuitive for me and suits my needs, it wont be what reverb I use that makes or breaks a piece.

Like I said IRs for cabinets is a different matter, I have a few options for tube pre-amp line outs as well as the line out on my Weber attenuator that all work very nicely with IRs

---

valhallasound - Sat Feb 25, 2012 2:17 pm

---

Here's a question: How much CPU does it require for a dynamic convolution algorithm to emulate the time varying Lexicon algorithms designed by Michael Carnes? The Lexicon plugins are well known to be low CPU.

Michael Carnes no longer works at Lexicon, BTW. However, he designed the algorithms for a LOT of devices while he was there:

PCM91
PCM92
PCM96
Lexicon 960
PCM, LXP, MPX plugins

I think the guy has a pretty decent understanding of acoustics. As does Barry Blesser. Smiley Face!

Sean Costello

---

Zaphod (giancarlo) - Sat Feb 25, 2012 10:38 pm

---

I owned and used a lot of lexicon devices, I think they are very musical, but realism is not their strongest point. There was a time they were the best (and only) thing availabe, and their particular sound was used in many productions we love. It doesn't mean they are accurate. Convolution techniques are way more accurate for a real concert hall simulation, IMHO. Try by yourself...

---

aciddose - Sat Feb 25, 2012 10:53 pm

---

i would think anything include any non-linearity whether made up of clipping, limiting or compression, waveshaping or saturation would have such an effect.

so you'd have to assume that any proper plate reverb would.

air is certainly non-linear with respect to the amplitude to frequency relationship. (waves should interact and stretch one-another.)

although this really isn't a A vs. B type discussion, in any case this simply isn't possible with convolution. whether or not it's been done in any particular algorithmic reverb doesn't really matter.

---

Zaphod (giancarlo) - Sat Feb 25, 2012 11:05 pm

---

we can, so it's possible (for example vnxt library). Whether or not it's done in other convolution based products doesn't really matter

---

aciddose - Sun Feb 26, 2012 1:29 am

---

you can produce hysteresis combined with an impulse? link the patent.

---

AudioGuy720 - Sun Feb 26, 2012 2:34 am

---

Both algo and convo reverb have their uses. I find GOOD convo IR's (Altiverb or Waves) to sound the most natural but algo is way more flexible.

---

whyterabbyt - Sun Feb 26, 2012 4:59 am

---

I thought real plate reverbs had at most two inputs?

Im talking about the 'different responses for instruments that are playing together'. That kind of dictates a discrete input per instrument, surely?

---

aciddose - Sun Feb 26, 2012 2:50 pm

---

sometimes i don't know if you're just being ridiculous or not, this time i'll go out on a limb and assume you really just had a brain-fart and didn't realize that any non-linear device will react differently when you input more than one component of a mixed signal. (for example, two guitar strings vs. one.)

for example, a distortion.

reverbs that take multiple inputs though? i've seen many of these which allow you to position both the multiples of inputs and outputs and use various virtual mic configurations. i'm not sure of any particulars because i've never used them though, maybe someone else can chime in on that.

---

Zaphod (giancarlo) - Mon Feb 27, 2012 11:06 am

---

there are pubblications around, google them, and check the technical page on our website, something was not pubblicated but you could guess it from there

http://www.acustica-audio.com/index.php?option=com_content&view=article&id=14&Itemid=133

---

whyterabbyt - Mon Feb 27, 2012 12:46 pm

---

[quote="aciddose"]sometimes i don't know if you're just being ridiculous or not, this time i'll go out on a limb and assume you really just had a brain-fart and didn't realize that any non-linear device will react differently when you input more than one component of a mixed signal. (for example, two guitar strings vs. one.)[/quote[

sometimes i don't know if you're just being ridiculous or not, this time i'll go out on a limb and assume you really just had a brain-fart and forgot the actual context raised by the poster I was addressing, who happened not to be you. To wit:



You might have started going on about 'non-linearity', but that's not what I had any interest in. Witter on about it to your heart's content, if you want, but Im asking something else of someone else, so perhaps you could stop pontificating to me about something irrelevant to me as though i missed your point.

Im interested in knowing which reverbs are actually capable of managing the soundspace of a full orchesta, instrument by instrument. And his reply made me think that Shy was talking about that too. So perhaps you'll let him speak for himself, instead of interjecting yourself in the middle of a question I asked him.



Next time, maybe just say nothing if you dont have an appropriate answer, then.

---

Hink - Mon Feb 27, 2012 1:27 pm

---

I may be way off base here but if I want to manage separate instruments within one instance of reverb I use the pan* for each instrument send them all to one stereo bus and apply the reverb there.

*or more accurately for me because it gives a 'forward/back' feel the 2 channel surround for each track in samp and a bus

---

aciddose - Mon Feb 27, 2012 2:34 pm

---

oh. well that's what he was talking about.

---

There are 32 posts in this topic.