convolution reverb removal

[aeroc]

I'm curious to know if there's any convolution software that you can use to take an impulse of a room and remove the reverb character from recordings after (or maybe even during) tracking. For the next month I'm living away from my studio and just have a small bit of equipment and would like to make the best of it. My room sounds terrible and I started thinking that I'm certainly not alone in that scenario. Seems like this "room subtraction" could be done to some degree but I've not aware of anything that could do it.

[Steamy Williams]

If it's possible you could really be on to something - that could be the best new idea for a product I've heard in a long time!

[aeroc]

It seems like the technology is already there and is implemented in similar ways. All you'd really need is a mix contol to bring take more or less of the room out as there could be strange artifacts popping up at %100 removal. I'm unsure whether the impulse grab could be made with the same mic as subsequent recordings without effecting the sound of that microphone but if that were possible you could set up your mic in the placement that you're going to record in, snap your impluse, and have a custom room removal for that exact setup. Move the mic, snap another impulse. I don't know the science involved, but it sure would be interesting if it worked.

[aeroc]

so.. if nothing exists, can anybody think of a workaround? can any existing programs be used to this effect?

[not_so_new]

Originally Posted by aeroc

so.. if nothing exists, can anybody think of a workaround? can any existing programs be used to this effect?

Yep

[cjmnash]

well, you could mic the room and put those mics out of phase....you'd probably have to move them around a bit to get them to be 180 out.

just an idea...i've never tried it.

chris

[dbbubba]

If you could do this (you can't by the way) a lot of shitty recordings could be made more listenable!

What you have not considered is that the reverberation is not only occuring after a note, but from the previous note DURING the note as well.
No algorythm could possibly distinquish information resulting from "bad" reverb from the "good" note.

It is all a stream of frquencies observed at a given moment, but our brain seperates it out into segments of time because of past experience with time.

It's kind of like un-mixing paint.

In fact, it is almost like attempting time travel if you really think about it!

You could possibly seperate stuff, but you'd destroy the stuff you intended to keep, too.

This idea/desire has been around ever since someone decided that the acoustics of a room sucked when they heard a recording played back.
Unfortunately, in the digital age people think that there might be some digital magic possible.

It is about as possible as removing the vocals from a recording.
It doesn't quite work does it?

Danny Brown

[FutureNerd]

Originally Posted by dbbubba

If you could do this (you can't by the way) a lot of shitty recordings could be made more listenable!

What you have not considered is that the reverberation is not only occuring after a note, but from the previous note DURING the note as well.
No algorythm could possibly distinquish information resulting from "bad" reverb from the "good" note.

It is all a stream of frquencies observed at a given moment, but our brain seperates it out into segments of time because of past experience with time.

It's kind of like un-mixing paint.

In fact, it is almost like attempting time travel if you really think about it!

You could possibly seperate stuff, but you'd destroy the stuff you intended to keep, too.

This idea/desire has been around ever since someone decided that the acoustics of a room sucked when they heard a recording played back.
Unfortunately, in the digital age people think that there might be some digital magic possible.

It is about as possible as removing the vocals from a recording.
It doesn't quite work does it?

Danny Brown

There's nothing impossible about deconvolution in principle.

Reverb (to a first approximation) is a linear process. That means that the original sound and the reverberations are simply added together. The fact that the reverb stretches out over multiple notes doesn't make the math harder. Given the convolution the original went through, there's a deconvolution that will exactly reverse the process and give you the exactly dry signal. Heh.

There are only two problems. The first is getting the convolution function of the room. You can put a speaker where you think the source was, and put the mikes where you think they were, and make sure all the people, instruments, props, windows, air temperature, etc. are exactly the way they were, and record known clicks or white noise with reverb, and calculate a convolution function. But problem one is that there was probably more than one sound source, it wasn't a point source, and it wasn't holding still and neither was the room.

Then you invert the convolution function to get the deconvolution. It's equivalent to a graphic equalizer with 44100 or 48000 or 96000 bands for every second of reverb. Problem two is that some of those bands will have very high gain. If everything were perfect, they would all cancel except for the dry original. But because of noise and limited accuracy of digitization, you get the noise amplified through these hi-gain bands in a way that doesn't cancel quite so well anymore. What has happened is that some of the information that would have enabled perfect reconstruction has been pushed down beneath the noise and sensitivity of the recorder.

So, because reverb is basically linear, deconvolution is only "n log n"-- not nearly as hard as descrambling eggs. But because everything's imperfect, the problem is worse than just measuring and undoing the room's reverb function.

I have never heard the simple version of this technique tried, so I don't know how well or badly it does. There are complex heuristic algorithms to try to deal with the noise in deconvolutions, but I don't know whether they've been applied to this problem.

There could also be heuristics to deal with multiple, changing sources and changing rooms. Haven't found any so far.

[Kiwiburger]

If anyone could do it, maybe the Celemony (Melodyne) guys could. If they can isolate notes in a polyphonic chord, and tune or shorten that individual note - what couldn't they do next?

I would have argued that was impossible to remove reverb - but maybe it isn't.

Our brain/mind has the amazing ability to be able to hear "into" mixed signals and filter out what we deem important. At some level, this is a form of data processing. As much as some would like to believe they understand how this all works, i'm convinced nobody has really got a clue.

So I would say it's possible in theory, because are brains are doing this all the time. If you are listening to somebody talking to you, walking around a hall, the mixture of reflections is constantly changing, but we subconsciously filter it all out and can follow the conversation effortlessly. We take it for granted because it's effortless - but at some level, there has to be some incredible number crunching going on. Or maybe it's pure analog, which would be more amazing.

[TLTD]

You would do the opposite of creating an impulse. Take a sine wav with reverb and use it in Deconvolver as "unprocessed" file, and the regular unprocessed sine wav as the "processed" file. Worth a shot...

[DITN]

Or you could try the SPL De-Verb.

[The Fold Studios]

Originally Posted by dbbubba

No algorythm could possibly distinquish information resulting from "bad" reverb from the "good" note.

Never say never. A lot of people were rubbishing Melodyne's DNA technology before it came out (I'm sure you could find plenty of posts on here by well informed people a couple of years ago saying that being able to seperate and manipulate componant notes from a single polyphonic audio file is impossible).

Apparently Melodyne are now working on technology to remove unwanted microphone spill so...

[paulpod]

is this the sort of thing you looking for?

ARC System

[steffo]

Originally Posted by The Fold Studios

Never say never. A lot of people were rubbishing Melodyne's DNA technology before it came out (I'm sure you could find plenty of posts on here by well informed people a couple of years ago saying that being able to seperate and manipulate componant notes from a single polyphonic audio file is impossible).

Apparently Melodyne are now working on technology to remove unwanted microphone spill so...

Thats like asking for a pill to cure unhappiness without side effects

Sure, melodyne can be a nice life but it doesn't sound very good.

[timlloyd]

In principle the deconvolution idea is possible, but putting it into practice and achieving decent results are very tricky.

In order to remove the reverb from a given recording, an IR would need to be made in the exact same room using the exact same mic, with the room containing the exact same things in the exact same places ... and people ... etc ...

In theory you could then use that IR to remove/attenuate the existing room tone from that one mic signal ... however I highly doubt that the results would be particularly good.

... basically just repeated FutureNerd
///

The only thing I've ever heard that can remove/attenuate reverb is the CEDAR DNS ... that works pretty well from the examples I've heard ... but only on voices as far as I'm aware, as that is what it's designed for.

[travisbrown]

Originally Posted by not_so_new

Yep

Okay. Tell me how you use a Transient Designer to remove reverb. I posed the question of removing reverb a while ago here when I got some live-recorded tracks that had way to much hall sound in them.

[MickeyMassacre]

Why not spend a few hundred bucks making the room not sound so bad?