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Old February 28th, 2007, 12:55 PM   #1
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2 LAV's--hearing audio in both

We had a studio studio shoot and we had 2 people speaking. They were about 3 feet apart and they were having a conversation. They were both wearing LAV's and the problem was that when person # 1 was speaking the lav on person # 2 was picking him up and vice versa. It was not too bad, but detectable with headphones on. It sounds almost like a slight echo, but when one or the other is turned off (L or R channel) it completely goes away.

What can I do to prevent this from happening ? If the answer is a pole mounted mic can you please recommend a decent mic too ? We are new to this type of audio set and I could use some suggestions.

Thanks !
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Old February 28th, 2007, 01:44 PM   #2
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Microphone polar patterns

Hi Jeff,

Try searching the net and Wikipedia to learn about the microphone polar patterns for omni, cardioid, bi-directional and shotgun mics: http://en.wikipedia.org/wiki/Microph...polar_patterns

Regards, Michael
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Old February 28th, 2007, 02:00 PM   #3
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Jeff,

Welcome to the unavoidable physics of sound.

Two open mics will almost always record two copies of any sound with a delay that is dependent upon the distance between the mics.

You've already noted the "post fix" for this. Simply cross cut between the channels of the mic you want to hear - and remove the parts of the tracks containing the echos. On today's NLE's it's not trivial, but it's a lot easier than it used to be in the analog days. Just take the audio track from one camera and cut the clips you want from it and delete the material from the distant mic. Then on a typical NLE timeline, if you simply move those clips over the other audio track they overwrite the second track and leave you with a perfect "switched" audio track.

As to the next time, some things to consider.

Yes, boom is one solution. It presumes you have a recording situation where you have access to a qualified boom op, or a boom rig with good enough off-axis response so that you can use a single boom to pick up both participants witht he quality results you're looking for. (Try to use dual booms, you'll have exactly the same problem you have now!)

Another approach is to use LESS sensitive lav mics. For example, I use both Sony ECM-77b's and ECM-44bs in my studio. The 77's are MUCH more sensitive than the 44s. So if I was doing a two-shot interview, I'd typically use the 44s precisely because they'd essentially supress the dialog of the second talent.

This is yet another example of why experienced sound folk are usually uncomfortable with questions like "what's the best lav mic for doing interviews."

Finally, If it's a fixed set, this might be a good place for a plant mic, a center located PZM or other fixed position microphone that picks up both participants equally.

A good recording is almost always the result of addressing a NUMBER of issues - because audio recording is fundamentally complex. It's not JUST about the Mic, or the Mic Placement, or the Room Dimensions, or the reflectivity of the Walls, Floor and Ceiling or the Room's Mechanical/Electrical Infastructure or the RF floating around - it's almost always about ALL these things and more.

That's what makes it so constantly interesting, at least from my perspective.

And what makes finally getting good results so fundamentally satisfying.

For what it's worth.
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Old February 28th, 2007, 04:39 PM   #4
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It's all in the pattern...

All Microphones are put into catergories of their pattern pickup. I have a couple of Shures that I use and they work great...but I have a specific pattern on them that "focus" what they hear. Hear are the descriptions of the differant patterned mics that are available:

Traits of Different Polar Patterns

Omnidirectional
All-around pickup
Most pickup of room reverberation
Not much isolation unless you mike close
Low sensitivity to pops (explosive breath sounds)
No up-close bass boost (proximity effect)
Extended low-frequency response in condenser mics. Great for pipe organ or bass drum in an orchestra or symphonic band.
Lower cost in general


Unidirectional (cardioid, supercardioid, hypercardioid, hemispherical, half-cardioid, half-supercardioid)
Selective pickup
Rejection of room acoustics, background noise, and leakage
Good isolation--good separation between recorded tracks
Up-close bass boost (except in mics that have holes in the handle)
Better gain-before-feedback in a sound-reinforcement system
Coincident or near-coincident stereo miking
Broad-angle pickup of sources in front of the mic
Maximum rejection of sound approaching the rear of the mic

Supercardioid
Maximum difference between front hemisphere and rear hemisphere pickup (good for stage-floor miking)
More isolation than a cardioid
Less reverb pickup than a cardioid

Hypercardioid
Maximum side rejection in a unidirectional mic
Maximum isolation--maximum rejection of reverberation, leakage, feedback, and background noise

Bidirectional
Front and rear pickup, with side sounds rejected (for across-table interviews or two-part vocal groups, for example)
Maximum isolation of an orchestral section when miked overhead
Blumlein stereo miking (two bidirectional mics crossed at 90 degrees)


From the sound of things, you are using Omni directional microphones. My Shures are cardiod and they work great. I use them on talent standing right next to each other in somewhat noisy enviroments with no problem.

hope this helps!
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Old February 28th, 2007, 05:47 PM   #5
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Lot's of great advice here.
Thanks very much for quick responses.
The lav's that we used came with the Senn evolution G2 set. I am not sure of what pickup pattern that wuld be, and I actually didn't know that there were different pickups for lav's.

Can one of you guys recommend a lav that has the characteristics we I am asking about ?

Thanks again for the thorough and quick responses.
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Old March 1st, 2007, 04:44 AM   #6
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Generally speaking omni lavs are less 'fussy' in use. The directionality of cardioids works against you as head movement by the talent takes them easily out of the optimum pickup direction and can produce noticable changes in voice timbre with movement. Cardioids are good for sound reinforcement situations where feedback is a problem but usually omnis work out better for interviews and dramatic dialog.

As others have mentioned, the best way to handle the spill between two mics is to send each one to its own iso track so you can mute all except the one speaking at the moment in post.

S
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Last edited by Steve House; March 1st, 2007 at 07:43 AM.
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Old March 1st, 2007, 04:41 PM   #7
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The mic element is what makes the lav directional or omni. On a lav, that would include the mic element itself and the cord running from the mic to the pack, as it sells as all one piece. For the Sennheiser Evolution mics you can get either the ME-2 omni mic or the ME-4 cardioid mic. They are completely interchangeable, so if you already have one with your kit (say the ME-2) all you have to buy is the other element (the ME-4) and use whichever element best suits each situation. You don't have to buy a new transmitter and receiver.

You don't necessarily even have to purchase a Sennheiser element, just because you have Sennheiser packs. As a matter of fact, some companies only make elements and you can purchase a model that fits the plug-in on your pack (different companies have different sorts of plugs). You can always mix and match - your favorite Shure element on your favorite Sony pack, etc., providing the plug of the mic matches the plug of the pack.

A couple of points about bleed (sound from one source appearing on the other source's track):
It will help if the location where you shoot has little or no reverberation or echo. If your subjects are close enough and loud enough, you will still get some bleed, but it helps.

Also, distance from the mic to the mouth plays a big role. The closer you can place the lav to the subjects mouth, the more you can turn the gain down and still get a good level and you will hear much less of the other subject. However, getting too close to the mouth can make the sound less natural (depending on several other factors) so it's a give and take situation. You can also use this in reverse. When shooting weddings, I often place the mic low on the groom's chest - where it meets his stomach. That way both he and the bride sound about the same on the track. If it was higher, the groom would be louder and his overall tonal quality would differ from hers.

I have to agree with Steve that omnis sound better for video, where feedback is not an issue. Of course good sound is not only about tone. Avoiding echo and room noise is also part of good sound. You have to weigh all the factors of each situation and choose the proper element for each use. It is true though, that every little movement of the head alters the tone of the speaker somewhat in a cardioid mic.

-Vence
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Old March 1st, 2007, 06:25 PM   #8
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Quote:
Originally Posted by Jeff Rhode View Post
We had a studio studio shoot and we had 2 people speaking. They were about 3 feet apart and they were having a conversation. They were both wearing LAV's and the problem was that when person # 1 was speaking the lav on person # 2 was picking him up and vice versa. It was not too bad, but detectable with headphones on. It sounds almost like a slight echo, but when one or the other is turned off (L or R channel) it completely goes away.

What can I do to prevent this from happening ? If the answer is a pole mounted mic can you please recommend a decent mic too ? We are new to this type of audio set and I could use some suggestions.

Thanks !
Hi Jeff,

Put 'em on separate tracks and cut out the off mic sections in post. Replace them with room tone.

Regards,

Ty Ford
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Old March 1st, 2007, 09:42 PM   #9
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An active mix can help this. Of course that takes an audio mixer that is comfortable in mixing audio and is fully focused on the program realtime.
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Old March 2nd, 2007, 05:55 AM   #10
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Thanks for all the great info. I will look into the Senn ME-4 and other lav's.
If there are any others that could be recommended I would appreciate it.

Regards.
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