Echo, dual lavaliers recording and editing

P

Publimix

Veteran
I recorded an interview, both persons had a omnidirectional lavalier microphone (Rode). The room had lots of echo.

In post each channel was good, not much echo. But after delivery to Vimeo, there was more echo to hear.

I think the reason for this was that I didn't mute the channel in post of the person who wasn't speaking. And that the combination of the two microphones introduced more echo.

Any thoughts or tips to prevent this?

thanks
 
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I would not claim to be an audio expert...but I think you've already answered your own question as to the solution.

Also, depending how the audio tracks of the resulting video was rendered (for Vimeo upload), perhaps you may have got an increase in apparent volume during compression/normalisation on each of the secondary lavs audio? This would effectively make the non-primary lavs sound louder than the original (as heard in your NLE master), thus enhancing the echo effect?

Bottom line, I always mute the non-used mic (and always have two on a speaker, where possible - in my case usually a Rode lav and another mic on a boom stand, simply selecting whichever sounded best during post and muting the back-up).

Just some thoughts. Now I'll sit back and let the real experts comment :)
 
Vimeo's encoders could have compressed the dynamic range as well. YT's encoders do some odd things to the audio... & video. Open mics add to an echoey sound. Use volume envelopes or expansion.
 
Yes, the other person's microphone picked up the speaker and presents a delayed copy. It also picked up reverberations from the room. The delayed copy causes a phenomenon called phase cancellation, which means it picks up the speakers voice out of phase and causes the voice to get distorted by virtue of combining the two signals. In live (broadcast) interviews, where we are using omni lavs, we always mute the non-speaking mics. Sometimes we have to leave them up and the phase cancellation can easily be heard. It's not pretty.
 
Publimix said:
I think the reason for this was that I didn't mute the channel in post of the person who wasn't speaking. And that the combination of the two microphones introduced more echo.

Any thoughts or tips to prevent this?
Click to expand...

Yep. Do mute the channel that's not in use.
 
This is one of the wonderful things about the Drugan automix on the Sound Devices 633 and 688. It will automatically mute and mix multiple channels which can really save a lot of time in post on roundtable discussions. But, yes, you really need to go through and mute any lav channels that are not being used. Lavs also have tend to have a relatively large amount of preamp hiss that can start to get obtrusive in even the quietest room when multiple channels are open.
 
The original 633 software builds did not have Dugan Automix either. It was added in a firmware update a while afterwards. That may be the case with the 10T. But I don't know for sure and SD ain't say'n at this point.
 
You need to do a dialogue editorial pass and then a basic dialogue mix. It's not enough to just mute the audio of the person that isn't speaking. You will get pops on the cuts. You need to have overlapping cross fades and you need to make sure the levels are pretty even throughout.

I wouldn't hold my breath waiting for automix to get put into any of the MixPre recorders. It's a big selling feature of the 6 series mixer/recorders and something that sets them apart from their lower cost brethren. I'm sure it wasn't something just given to Sound Devices. They may have had to pay a hefty licensing fee or something like that. Awesome tech ain't cheap.
 
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