Is it possible to cancel echo?

farss wrote on 12/15/2003, 12:00 AM

Yes I now this would be more appropriate in the audio or SF forum but there's usually a few more people awake here.

A frined of mine shot video of an outdoor event. He had to shoot stills while someone else used the video camera. Problem was the PA guy turned the audio down on on the front speakers so the sound the camera picked up was mostly what bounced around the venue. Needless to say the echo is so bad as to pretty well render the voice unintelligible.

So I'm wandering anyone had any success getting rid of echo?

As always I'm only too well aware of how easy it is to add things, getting rid of them is another matter, my gut feeling is this borders on the impossible. I've already EQed as much out as I can and whacked in heaps of compression, it sounds pretty aweful but the intelligibility has improved. Hoping someone know of a better solution. I know echo cancellation is used on phone circuits with great success but there it's a single fixed delay not multitap delays.

Comments

Grazie wrote on 12/15/2003, 12:40 AM

Nasty!

Is there a separate recording of the event - say from the Sound Guy? This wave shift profile is a real bummer. Maybe there is some software that allows one to "sample and then eradicate? I don't know. As you say, one can easily "add" echo" in the various Audio FXs we got . . but that ain the thing you are wanting . . I'll give it some further thought - yeah?

Grazie

farss wrote on 12/15/2003, 12:56 AM

Grazie,
thanks. There should have been a separate audio tape. Ha!

All of the worst problems I've had with audio is with feeds from the desk.
The audio guy is aiming to balance out the sound in the auditorium not make an accurate recording.
Comments are usually somethig like "but the drums were already loud enough" or "Oh sorry, yeah that was a foldback feed so didn't have the compares mic".

I just tried using Wave Hammer on it in SF. well it's sure bleeding load enough now!

Grazie wrote on 12/15/2003, 1:11 AM

Oh dear!

There has to be a way with some fancy s/w to sample a wave form. Graphically edit that wave form and either remove OR better still, move that wave form so that it matches up with the other? This would then at least cancel out the other? Is there a way to just accept DBs of a certin level/height? If you made the the thing very quiet, then did a "physical" rerecord off of the loudspeaker - yeah I know it's a bit amateur, but that's me to a "T"? Could you physically "muffle" the recording space as you were recording? I can think of lots of ways to "introduce" white noise that could be used so as to "filter" out what wasn't needed. Could you "boost" the sound and then physically record with a mic in a corner? Okay you'll look odd - do it behind closed doors so you wont be noticed! - There must be a way to do this. Sometimes we all get a wee bit s/w driven too - yeah? - I suppose, whqat I'm saying is think "around" the problem, in a more real World way. Apart from the above, I'm having difficulties. As others"wake up then maybe they will either larf at me OR Ignore This User, in digust . . hey ho . .was it ever thus . .

As a result of your post I too openned up SF7 and did a look see . . Yup, Hammer is there . nothing about Echo reduction - PLEnty of ways to add Echo e c h o . .. e c h o . .

Any good?

Grazie

farss wrote on 12/15/2003, 1:49 AM

After I dropped out all but the necesary frequencies and then 'hammered' it real hard it'll probably be OK. It would hav helped if:

a) The kids weren't making such a racket.
b) People could learn to speak INTO a microphone.

It's not really my problem anyway, just trying to help out a mate, no one can say I'm parochial, he's cutting it in FCP!

If there's one thing I freak out about shooting these live events it's the audio.
If I ever do another one I'm going to have at least an 8 track recorder and stick my own mics on anything that looks like it might open its mouth.

I'm just going to go with what I've done, he's got to show it to the client in two days and I do have other stuff to work on...
Next project...very wobbly camera work and it's all basically a locked off shot on a tripod. Oh and yes they screwed up the audio as well..
Maybe I need to look at that stuff from Dynapel.

Grazie wrote on 12/15/2003, 2:21 AM

Farss! LArf . . nearly fell off me chair when you said about sticking mics everywhere you could . . Yes, I'm the same about audio. . . GOOD audio can make an average video viewable. .BUT bad audio truly KILLS a good vid - yeah?

Oh yes Dynapel. It works. It's cheap. If I can use it ANYBODY can. Dead simple. However I've been rather imnpressed with the SteadyMove package. Unfortunately only for Premmi users. I've emailed them to make at least a standalone, so we could try it out. If you've got Premmi, consider SteadyMove too. Go see their website. It is very good. And until I 've seen it work with my setup - via a demo - I'm having to stick with Dynapel's SteadyHand. - As I say, it's cheap and works if you haven't got truly very very dodgy movements. If you want I could Dynapel it for you - interested? It's a boring job, but hey, someone has to do it!

Grazie

Grazie wrote on 12/15/2003, 2:23 AM

If you wanna see the dif I'll give it a go and return it - yeah?

G

farss wrote on 12/15/2003, 3:04 AM

I'm just capturing it now Graize.
Looks like the whole 90 minutes of it the camera was mounted on the head of one of those bouncing head dogs people used to put on the back shelf of their cars.

Oh and for the first few minutes the cameraman keeps adjusting the focus.
This time I'm going to charge more to fix it than they would have paid me to shoot it right the first time.

Grazie wrote on 12/15/2003, 3:18 AM

HAH! - Nodding dog syndrome . . great . . . judicious use of K/Fs in Track Motion . . cooooo .. could take sometime . . . wanna hand? The focus is gonna be a beach ..

Grazie

farss wrote on 12/15/2003, 3:26 AM

Thanks for the offer Grazie BUT...
It's 90 minutes of the stuff, later parts look OK.
I just downloaded Dynapel demo just to see how much work it entails.
If it needs keyframes then forget it!
If it can lock onto a sharp transition like the stuff in Avid the it may do the job.
The demo videos look impressive, but of course they don't say how much work it took!

TorS wrote on 12/15/2003, 4:58 AM

If you keep the original echoy track and combine it with a manipulated track you can probably be more drastic with whatever manipulations you do. Have you tried noise gate?
Tor

Spot|DSE wrote on 12/15/2003, 7:21 AM

Acoustic Mirror is good for this, it can be used as a second track, with the impulses applied negatively to the audio, and certain sounds taken out. It's a tough process no matter what, but it can be done. However, as we say in the studio, "You can't polish a turd, it's still a turd underneath all that stuff."

Randy Brown wrote on 12/15/2003, 7:50 AM

Hi farss,
>>If I ever do another one I'm going to have at least an 8 track recorder and stick my own mics on anything that looks like it might open its mouth.<<
You probably already know this farss, but if the sound man knows what he/she is doing, they can send you an audio feed from the board. This, along with another track, connected to a mic, can give you something to work with in post. If your cam has at least audio 2 tracks you wouldn't even need the recorder. Good luck with your friends' problem BTW.
Randy

musicvid10 wrote on 12/15/2003, 8:27 AM

I don't know if my technique will help because it sounds like the reflection is pretty bad in your case, but it may help a little. Here it is here for you to try:

http://www.sonicfoundry.com/forums/ShowMessage.asp?Forum=4&MessageID=140867

farss wrote on 12/15/2003, 12:23 PM

Thanks to everyone for their help.
I'm going to spend a bit more time on it in the next few days, more as a training exercise. I really cannot do much more with it at the moment, got to much else happening for paying customers. And just for laughs the copy of the section that my mate gave me to fix up the audio has got a nasty head clog in the middle of one section where he needed the audio fixed.

Spot|DSE wrote on 12/15/2003, 7:17 PM

Musicvid, this is the same technique employed by using the Acoustic Mirror.
If you know this technique for tape, you've been around for a long time....Stevens even had an 'automation' setting for this on their consoles about 25 years or so ago. Longer than many of these VegHeads have been around. Or walking, anyway. Don Davis taught this at AES one year. It's a valuable workaround. Interestingly enough, it's also the same technique used in a slightly different fashion to remove noise/artifacts from a video stream.

MUTTLEY wrote on 12/16/2003, 2:19 AM

Farss, would love to hear how Dynapel, or if you have the time post some before and afters. I've usually got a pretty steady hand but for the price it seems like this might be a good product to have in my arsenal.

- Ray
ray@undergroundplanet.com
www.undergroundplanet.com

farss wrote on 12/16/2003, 3:23 AM

I've well and truly given up on this project. It's rendering out now prior to PTT.
I cannot believe what these guys managed to do.
They had a SVHS camera, a SVHS VCR and a feed from the desk. They took the video out from the camera into the VCR via a LONG run of cable. They've fed the feed from the desk straight into the unbalanced inputs of the VCR.
Then they had one VHS tape and one SVHS tape. So they put the VHS tape in the camera and the SVHS one in the VCR.
So they ended up recording the best video they had at VHS quality and the feed with all the highs missing on SVHS. Except somehow the audio from the desk only got recorded on the linear tracks on the VCR and then with so much AGC that every time the level drops the hum comes up to greet you, not that nice clean 50Hz kind of hum, it's those nasty spikes you get from dimmers that you just cannot EQ out. Yes I know NR will probably get rid of it but due to a special deal from Sony I got SF but no NR, yet!
And just to make the job that much easier they stopped and started recording at different points in the show on the VCR and the camera, not that I'd expect two VHS machines to come within cooee of holding sync for 3 hours.
At least they took some cutaway shots....except they clearly show there's no one on the stage.

Sorry, this is pretty boring really, just wasted untold hours on this and for almost no financial reward. I should have known it wasn't going to go well. They couriered the tape to me last week, when I went to capture it I found they'd sent me a blank tape. Odd thing though, someone had taken the record enable tab out.