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Old February 6th, 2007, 06:15 PM   #1
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Echo. Removing echo that is.

I've got some studio footage (think evening news) where one mike was turned too low or running down its battery AND that guy's audio has a bit of echo because his voice is almost as strong in his co-anchor's mike. There is only one speaker at a time. I'm using FCP and wondering if there is any simple way to *remove* the echo. my audio is already mixed together, no option to separate the different speakers at this stage, alas. Audio, as always, is the most challenge part of this whole deal!
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Old February 6th, 2007, 06:48 PM   #2
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Originally Posted by Jim McQuaid
I'm using FCP and wondering if there is any simple way to *remove* the echo.
Sadly no. Reverb is the hardest thing to get rid off, it's nearly impossible to do so without destroying the audio. You could try an expander but ultimately you're better off re-recording the audio separately or something.

Bummer eh :(
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Old February 6th, 2007, 07:35 PM   #3
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About the only thing you can do it to find the dominance resonance of the reverb, and cut that frequency a bit. It won't fix it, but it can help remove some of the reverb's signature.
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Old February 6th, 2007, 10:54 PM   #4
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I've done it with a fair degree of success, the technique goes way back to the days of analogue tape although it's way easier in the digital domain.

Basically you make a copy of the track and invert it. Now you have 100% cancellation. Now apply compression to one of those tracks. Trick here is to get the knee of the compressor so that the compressor is just compressing the wanted part of the signal and not touching the lower volume echo / reverb. So now the echo will still cancell out but the compression will alter the wanted part of the track so it doesn't get cancelled. Adjust attack and decay times of the compressor to taste as well as the level of one of the tracks. Adding Eq after the two tracks are mixed as well will help.

You'll never get it 100% as good as it would have been minus the echo but you can make a very signifcant improvement.
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Old February 7th, 2007, 12:52 AM   #5
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Interesting technique, Bob,

I would guess that if the space was relatively dead (the reflections have LF content, but little HF content), you could also low pass the inverted, compressed track. That would ensure that none of the HFs are removed from the original.
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Old February 7th, 2007, 04:14 AM   #6
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There is a technique I have used a lot in the studio (my real job is being an engineer/producer - video is my new hobby/passion :D )

It involves a device called the 'SPL Transient Designer' This unit is great and often a life saver in the studio. It comes in 2 and 4 channel versions.

Basically what it does is either shorten the decay time of the sound (and thus getting rid of too much verb without destroying the sound too much) or give more 'attack' to a dull sound (e.g. dull, cardboard sounding percussion or drums, violins that need more 'bite' etc.)

In your case, if you only need it once, it might be usefull to see if you can rent or demo a unit.

Hope this helps
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Old February 7th, 2007, 04:53 AM   #7
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Quote:
Originally Posted by Jon Fairhurst
Interesting technique, Bob,

I would guess that if the space was relatively dead (the reflections have LF content, but little HF content), you could also low pass the inverted, compressed track. That would ensure that none of the HFs are removed from the original.
I've used it twice on speech, once it was a shoot in a very high atrium that was all glass and marble and only the on camera mic was used and it worked very well. I wouldn't say the results were spectacular, just enough to make the speech bearably intelligable. You might be able to achieve much the same with a good gate but I didn't have one at the time to try.

I'd hazard a guess that if it was music it'd be useless.
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Old February 7th, 2007, 06:00 PM   #8
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Thanks!

I will try the "cancellation" technique and look into the SPL transient... unit as well. I really appreciate the learned suggestions. My original is of decent / passable quality, so if I can engineer a "slight" improvement, that should be quite serviceable.

Thanks to all.
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