What's the best way to avoid audio clipping?

smhontz wrote on 1/11/2006, 8:06 AM
I have a Sony VX2100, a Studio 1 XLR-BP Pro adapter, an AT899 omni lav, an AT831 cardiod lav, an ATR35s omni lav, and a Calrad 10-10 shotgun mic. I shoot interviews and dramas for our church. I use DV Rack where possible to monitor the shoots. It lets me know if the audio clips.

My question concerns how to best avoid audio clipping. In an interview setting, or a one-person drama, I use one of the lav mics, going into the Studio 1, and then into the Sony mic jack. If I have several people in a drama, I might use the shotgun mic on a boom over their heads, going into the Studio 1, and then into the camera.

Interviews aren't really a problem, because the levels are fairly consistent. I can adjust the volume at the Studio 1, or at the camera by using the manual audio levels. But in a drama, sometimes the actress is whispering, and sometimes she's shouting, and I can end up getting clipping.

So here's the questions: if I know I'm going to have a wide dynamic audio range in a shoot:

1. Is it better to leave the camera on auto audio gain, and let it control the levels?
2. Would one mic be better than another in this situation?
3. Would changing the mic placement help (typically the lav is on a collar or down on the shirt a bit if they have a button-up shirt)?
4. If I use the camera in manual audo mode, is it better to back the sound off at the Studio 1 (a passive device), or is better to use the manual audio level controls on the camera?

Comments

Jay Gladwell wrote on 1/11/2006, 9:19 AM

Do not use "auto levels" or your sound will rise and fall as the subject speaks and doesn't.

If I understand you correctly, what you need is another person--a sound recordist to ride the levels as you shoot the video.


lotus wrote on 1/11/2006, 9:30 AM

use an audio limiter
daryl wrote on 1/11/2006, 1:39 PM
Jay is right about the sound fluctuations with auto levels on. I have, however, in a pinch, set the transmit levels of the transmitter pretty low. I get good levels on tape without the "ups and downs" of volume when speaker is speaking or not. Be sure to do a sound check with headphones and check the meters. The other options listed in this thread are better, but you might try this in cases that justify it.
farss wrote on 1/11/2006, 1:59 PM
Biggest problem I can see is the rather poor audio of the VX2100, combine that with recording only 16 bit audio and you really don't have much room to move.
A much better approach is a field recorder with even average mic preamps and recording at 24/48K. Then you can set your levels so that you've got plenty of headroom and adjust levels, apply compression etc in post.
Simply using external preamps and limiters etc mighn't gain you much as from memory on the VX2100 you've only got mic level inputs which are always adding their own noise floor. At least on the PD170 you can switch the inputs to 'line' thereby reducing the amount of noise the camera is adding to the mix.
Bob.
Grazie wrote on 1/12/2006, 12:05 AM
Another reason, back in 2002, why I bought my first DV camera: Canon XM2 has Mic Attn, auto AND manual for channels with 2 dials one each channel PLUS each channel is monitored in eye piece and LCD flip out.

Grazie
seanfl wrote on 1/12/2006, 1:30 PM
Most of the newer camera do a better job of not trashing the sound with auto levels. In the past, cameras would "suck up" tons of room noise if there wasn't much audio to be heard (say a quiet part of your interview recording). Now most that I've tried have a higher threshold and won't do that as aggressively.

So, I've found for interviews and the like, it's much better to use the auto levels and have a consistent level on tape. It's not really a levels going up and down effect, more of a smaller dynamic window (audio compression) that's going on. Some higher end cameras have settings like agc (auto gain control) or limiter. The limiter only kicks in when the levels get so hot they would normally clip. You could use the limiter and it wouldn't touch the levels unless they got really hot.

Compression / agc can be your friend in many situations...I also recognize that if you have the equipment and know how to control your dynamics in other ways, you can get better sound. I'll take some compression artifacts from the auto-leveler any day over digital clipping.

Sean
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