remove room acoustic echo from a recorded live theatre event

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loninappleton
Posts: 85
Joined: Wed Jul 07, 2004 3:55 am

remove room acoustic echo from a recorded live theatre event

Post by loninappleton » Sun Sep 17, 2017 1:38 am

I have a project to correct. I'm not a professional. The piece of audio however is a
professional production of a stage play. There is room echo in all of it. Or perhaps a microphone placement
in the theater house which has produced an unnatural echo effect. Not singing in the
mountains bounceback but noticeable in every word.

Is there some sort of 'anechoic filter' ( if that is the right term) to process the whole
two hours plus wave form for flat natural human speech? Goldwave is the most complete software I know of
but I don't know where to begin for such a question as I am not working in the
audio field. I do my projects as hobby.

Tristan
Posts: 322
Joined: Mon Jun 01, 2009 8:20 pm
Location: Southeast Michigan

Re: remove room acoustic echo from a recorded live theatre e

Post by Tristan » Sun Sep 17, 2017 12:03 pm

loninappleton wrote:I have a project to correct. I'm not a professional. The piece of audio however is a
professional production of a stage play. There is room echo in all of it. Or perhaps a microphone placement
in the theater house which has produced an unnatural echo effect. Not singing in the
mountains bounceback but noticeable in every word.

Is there some sort of 'anechoic filter' ( if that is the right term) to process the whole
two hours plus wave form for flat natural human speech? Goldwave is the most complete software I know of
but I don't know where to begin for such a question as I am not working in the
audio field. I do my projects as hobby.
You'll have to make do with a noise gate, I think, and do what you can at the end of spoken words and phrases. A real-time de-echoing filter would need an adaptive mode to be effective, and it's hard to adapt to something that's inherently inconsistent.
If I can read the manual, so can you.

loninappleton
Posts: 85
Joined: Wed Jul 07, 2004 3:55 am

Re: remove room acoustic echo from a recorded live theatre e

Post by loninappleton » Sun Sep 17, 2017 1:07 pm

Thanks for the reply. I'll look up the noise gate in Gw but it sounds like there's no real fix
for it.

I normally use a free tool called The Levelator to bring up voice and suppress things like
tympani in battle scenes etc.

But from what you say there is no 'marker' in pitch or sound that can be altered.

Tristan
Posts: 322
Joined: Mon Jun 01, 2009 8:20 pm
Location: Southeast Michigan

Re: remove room acoustic echo from a recorded live theatre e

Post by Tristan » Sun Sep 17, 2017 1:36 pm

The only thing that's consistent in your file echo is time, so time is the only thing you can manipulate effectively, and then only under certain circumstances.
If I can read the manual, so can you.

DougDbug
Posts: 2030
Joined: Wed Feb 16, 2005 3:33 pm
Location: Silicon Valley

Re: remove room acoustic echo from a recorded live theatre e

Post by DougDbug » Sun Sep 17, 2017 11:24 pm

Chalk it up as a learning experience. :( Next time you'll know to get the microphone closer for more direct-sound and less reflected sound.
which has produced an unnatural echo effect.
Actually, reverberation ("reverb") is natural and it can sound great with music. But, what sounds great live in a big room, coming from all directions, sounds unnatural coming from a pair of speakers in a small room.

Your brain is also more-able to ignore noise (rattling papers or coughing, etc.) live and it becomes more annoying when played-back in a recording. ...If you've ever used a video camera you've probably noticed that the noise sounds worse in the recording that it did live.

raygrote
Posts: 14
Joined: Tue Aug 27, 2013 12:04 am

Re: remove room acoustic echo from a recorded live theatre e

Post by raygrote » Thu Sep 21, 2017 6:47 pm

Yep, as others have said, once it's far away, it'll always be far away. Though there are a few things you can try.

First, there are now vst plug-ins which can try to suppress or boost the reverb, and which do so using intelligent algorithms designed for this purpose. Gold Wave can support VST Plug-ins, though I haven't tested many plug-ins with it. Most should work, though. The three hot ones right now are the DeReverb module as part of Izotope's RX Restoration suite, Zynaptiq's Unvail, and Acon Digital's Deverberate. I believe the latter, the one from acon Digital, is the least expensive, but the demos didn't sound bad at all when I heard them, and that was just shy of its 1.0 release or thereabouts and it's been several years since then, so the algorithms have been improved. As is the case with any ambitious tool, the algorithms can sound very different and have their own strengths and weaknesses. I'd encourage you to, if you can, try all of them. To my recollection they all have trials so you can freely test each one and compare.

One thing to keep in mind is that these algorithms work, at least in part, by attenuating background or similar characteristics, and emphasizing foreground or different characteristics. Reverb has a sameness to it, and so it is often fairly easy to swallow up by a capable algorithm. But there are limitations. Since background noise or lingering decaying sounds like timpanis often have a sameness too, they are often reduced and muted a bit if you allow the algorithm to be too sensitive. So, it is always a trade-off between giving the signal more focus and clarity versus swallowing everything that makes it breathe. Don't just expect magic!

If using an external plug-in won't work, then I have one more trick up my sleeve. Gold Wave actually does have a crude algorithm for removing reverb though it is likely not intended to be used as such. I discovered this by accident nearly 10 years ago. If you use Gold Wave's noise reduction, and you set the reduction envelope to use average, it will basically do what a reverb suppression process would do: remove static components of the audio and preserve the differences. While it's only meant to reduce background noise, the average algorithm is extremely sensitive and can be pushed hard. Very hard. To get the best results though, set the FFT size to something high, I recommend at least 12, if not 13 or 14. The longer FFT sizes sound less metallic and tinkly but keep more of the room space in. A smaller FFT size will remove more of a sense of space but the tinkly effects of the processing will be more noticeable. The overlap makes little difference in my experience, though feel free to play with it. The scale percent should be set as low as possible to reduce the room reflections to a suitable amount, and no higher. That's pretty much it! Because it's not meant for reverb reduction, you'll get artifacts from using it this way, probably a lot more than you'd get from a dedicated algorithm designed for the purpose. Gold Wave has no intelligent way of actually determining what is and isn't reverb like dedicated products may, so it's not a replacement for them. But it's at least an interesting little thing that Gold Wave can attempt.
Last edited by raygrote on Thu Oct 26, 2017 4:45 pm, edited 1 time in total.

loninappleton
Posts: 85
Joined: Wed Jul 07, 2004 3:55 am

Re: remove room acoustic echo from a recorded live theatre e

Post by loninappleton » Thu Sep 21, 2017 9:54 pm

Thanks for the detailed tricks up your sleeve. :-)
I have used VST very little and only (as I recall) for playback in Foobar.

I will review carefully what you have on the settings to work with Goldwave.
I know however that this is a longshot trying to strip out what amounts to
every syllable of dialog.

Thanks for answering.

DewDude420
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Re: remove room acoustic echo from a recorded live theatre e

Post by DewDude420 » Wed Sep 27, 2017 11:47 am

The process of removing this kind of echo is called "deconvolution". It's the opposite of convolution, which is a process of creating echo using an "impulse response". Basically you set up microphones in a room and create a sharp impulse....like a clapper or baloon pop. You then record the echo of the room. That sample is used to convolve the audio to match the echo.

Deconvolution is very difficult. It was tried in the 70s and has remained in the realm if super expensive professional or forensic software.

The only software package Ive seen this feature in (but never tried) is iZotope RX. Goldwave unfortunately does not have the effects that would be required. You might mitigate some of it by isolating the "center" from the audio..which Goldwave does have suppory for.

raygrote
Posts: 14
Joined: Tue Aug 27, 2013 12:04 am

Re: remove room acoustic echo from a recorded live theatre e

Post by raygrote » Thu Oct 26, 2017 4:44 pm

Sorry for bumping this thread, but I just came back to it and saw that it had gotten more replies.

DewDude420, I'm really curious about deconvolution. If I understand right, you somehow estimate the reverb, get an impulse with that, and try to remove that reverb from the signal by doing an inverted convolution of sorts, in effect trying to mathematically cancel the reverb out of the signal, rather than resorting to high level algorithms that just rely on estimation? This seems really intriguing. And I can see why it would be nearly impossible. However you say that RX has deconvolution or at least attempts it. I've played with RX a bit, but have never seen mention of that, even in the RX advanced manual. Any pointers on where it might be? Is it by chance the dereverb module you're talking about? If so, then I think that is more estimation-based and not convolution-based.

loninappleton
Posts: 85
Joined: Wed Jul 07, 2004 3:55 am

Re: remove room acoustic echo from a recorded live theatre e

Post by loninappleton » Thu Oct 26, 2017 6:24 pm

I will stay tuned to this as well. I haven't gotten to that particular job since OP.

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