2 Camera Audio Echo

[vt2la]

Hello people, just registered with the forum but I've been using it as a valuable resource for a few months now. Here's my dillemma.

I've been shooting a lot of 2 camera set ups with the HVX lately, running two sennheiser lavs into one camera, and a sennheiser shotgun mic into the other. The problem I've been having is that when I bring the footage into Final Cut and try to lay the audio from both cameras over each other, no matter how close I get them, there is usually a slight echo, but not always.

First of all, why does the echo occur in the first place? Secondly, why is it not consisten? Thirdly, and most importantly, how can I get rid of it?

Hope you all can help.

[Barry_Green]

Are the lavalieres on the actors, and the shotgun is a long distance away? If so, you may be running into issues with the speed of sound; sound arrives at the lavalieres instantly but doesn't hit the shotgun until a frame or so later. If this is it, then you'll notice more echo when the actors are further away from the shotgun, and less when they're closer.

[ozduc]

The distance certainly sounds like the problem. You will also get a delay on the audio from the onboard mic compared to the lavs. For every 1ft. your camera is away from the subject, you get about 1 milisecond of delay. Move back 100 feet and you now have approximately a 100 millisecond delay with the onboard mic. That is 1/10 of a second or 3 frames when shooting 30 FPS.
To solve the problem you can delete audio tracks 3 & 4 or move them earlier to compensate for the delay. The only problem with this is if the camera was moving around then the length of the delay will be constantly changing, which sounds like was the case with your camera mounted shotgun mic.

[vt2la]

thanks for the suggestions guys. distance could be the issue in some of the cases, but I've been shooting in situations with a boom mounted shotgun going into one camera, and two lavs going into another. The lavs were attatched to actors sitting about two feet from one another and it was a tight shot so the boom was only a foot or so away from their mouths. There was still an echoy effect after I take away tracks 3 & 4 and lay the remaining tracks over each other as close as they can get to perfect. It doesn't leave an actual echo when you get it really close, but it makes the voices sound robotic.

[wgzn]

i have to ask. why THREE mics to begin with?

id bet money that one of the problems youre having is the TWO lavs. each persons lav is going to hear both their voice AND a softer slightly delayed version of the other persons voice nearby. so at any time, youre getting one strong voice from the speakers mic and a very slightly delayed softer sound from the other persons lav whos not speaking at that moment - and vice versa when the other person speaks. layer on top of that the delay from the boom shotgun and youve got all kinds of room for delay/echo issues

[vt2la]

it's definitely not the lavs that are causing the echo problem. when I just leave the two lav tracks together there is no echo issue at all. often times the echo comes when I have just one lav track from camera A, and the boom track from camera B on top of each other.

at this point I'm fairly sure it has to do with the two cameras recording the sound at slightly different times, so that in order to make them fit perfectly, you would have to be able to move the audio a fraction of a frame in the editing program.

to clarify, I've never had the echo issue occur from sound that all came from the same camera, for instance, when I have the two separate lav tracks combined with the internal microphone (which I ultimately get rid of anyway) the echo does not occur. It DOES occur when I'm combining the sound from a second camera with the sound from the first camera. Whether it be lav or shotgun, or even the internal mics.

[ozduc]

Ok so you've narowed it down to the fact it only happens when youo combine the footage from the 2 cameras. If that's the case I'd have to ask how are you syncing the footage from the 2 cameras?
BTW the robotic sound you hear is probably a phasing issue.

[vt2la]

I haven't been doing anything in camera to synch the two cameras, is that absolutely necessary to avoid this issue? From now on I'm going to use a 1394 cable, I think it will solve most of these problems. I'm not familiar with phasing, what's it all about?