removing echo on audio

[fredjeang2]

Hi,
I've been talking to a few sound engineers
1 from broadcast and 1 from a recording Studio,
About the possibility to remove echo
In post and both were telling me that it's
Extremely difficult and that should be treated
On set by profesionals because it's One of
The really tricky issue in post production, even
Today.

It seems that it involves doubling the tracks
With invertion in one then a serie of complex
Manipulations on the frequencies etc...
I mean, not a filter is capable of straight solution
And it involves specialist knowledge. And even, results
Aren't guaranteed.

Do you confirm that?

[Christopher Sanderson]

Extremely difficult indeed. The engineered solution suggested is well beyond my pay grade. My only effort would involve fairly heavy compression which may lessen the echo but not remove it - it depends on the relative strength of the echo vs. the main signal. If the original recording mic was nice and close to the speaker, it will be easier than a more distant boom mic that inevitably will have picked up more ambient and reflected sound.

I think the easiest solution is to replace with post-synch. There are voice artists who can do this really well.

[Sareesh Sudhakaran]

An echo can be removed easily because it is distinct - you just have to chop it off.

But reverb? No. It is impossible with today's technology. I have never seen anyone remove reverberation without it being very obvious.

It will be very obvious when cut with 'good' audio before and after the fact. Like Chris said, better to redo it from scratch. Then you can add room tone, noise, filters, etc. to get it to match.

[fredjeang2]

Thanks guys.
Fortunatly this is on a "repairage" in
An interior that is an iron structure
Within a Long corridor and the reverb
Was horrible, to the point that it gave
Headache just When talking.
It was recorded with a boom.
Back in the Studio I tried to see if I
Could do something with Audition and
Nothing. You both confirm what sound
Guys told me.

[John.Murray]

Actually it is possible via deconvolution, but probably not practical (relative movement of source, microphone and environment)

http://cnx.org/content/m45389/latest/?collection=col11475/latest

[happyman]

You could give SPL De-Verb a try:
http://spl.info/index.php?id=463&L=1

Unveil is a great tool but a lot more expensive:
http://www.zynaptiq.com/unveil/videos/

[fredjeang2]

yep,

What the sound engineers told me is correct. Although there is to date no easy cure, the invertion is the base to re-work the reverb "removal".

It's doubling the stereo track, inverting the doubled one so the sound is completly cancelled. Then re-work the frequencies (re-create) from both so you obtain a very flat mix, leaving cancelled the frequencies where the echo is most present. (no possible real cure with today's tech for serious reverb)

then do a mixdown and from the mixdown, recuperate the frecuencies that have been canceled previously. As the reverb is "sort of" removed, the rebuilding equalization of a decent sound is possible.

It's not an easy turnarround, to a specialist level, but this is the path and with a bit of patience a lot can be fixed if the reverb is not too harsh.