Audio Levels and Distance at DVinfo.net

Ben Hillier · October 1st, 2007, 11:06 AM

Situation: In a documentary context using on camera microphone - Shooting general scene of people up close then from a distance approx 20 meters. Catching inteligable words not important.
Question? What are peoples general method of setting audio levels? Is it best just to leave them at level for close up, or is it best to ajust them for each shot? Or best auto gain in this situation?
Just want to get some takes on that, thiking what would cut togther best ect. Cheers. Ben.

Michael Nistler · October 1st, 2007, 12:23 PM

Quote:

Originally Posted by Ben Hillier

Situation: In a documentary context using on camera microphone - Shooting general scene of people up close then from a distance approx 20 meters. Catching inteligable words not important.
Question? What are peoples general method of setting audio levels? Is it best just to leave them at level for close up, or is it best to ajust them for each shot? Or best auto gain in this situation?
Just want to get some takes on that, thiking what would cut togther best ect. Cheers. Ben.

20 meters is way too far to use an onboard mic to catch audio, even with a shotgun microphone, talent speaks loudly, always faces camera, etc. At that distance, you need an XLR cable and boom mic or else use a lavalier. Keep your camera within 3 meters. Remember the inverse square law - ever time you double the distance (3 meters to 6 meters) you get one quarter of the sound (not one half). At 20 meters the sound is very hard to hear and easily obscured by the environment - cracking up the signal in post will also be amplifying the noise. Indoors is bad too, picking up all the echos of the walls, floors, ceiling.

Good luck, Michael

Steve House · October 1st, 2007, 01:21 PM

Quote:

Originally Posted by Ben Hillier

Situation: In a documentary context using on camera microphone - Shooting general scene of people up close then from a distance approx 20 meters. Catching inteligable words not important.
Question? What are peoples general method of setting audio levels? Is it best just to leave them at level for close up, or is it best to ajust them for each shot? Or best auto gain in this situation?
Just want to get some takes on that, thiking what would cut togther best ect. Cheers. Ben.

About the only thing you can do at that distance with ANY mic, regardless of price, is unintelligible crowd babble called "walla." Indoors even that might not be possible becaise of excessive reverb. I can't think of anything you could do that would give you material that would intercut smoothly with audio recorded close-up.

Ben Hillier · October 2nd, 2007, 02:19 PM

Thanks for your replies. I`m not hoping to get any inteligable vocies, just get atmos. Abviusly I do pick up atmos at 20 meters, just sounds real quite, and wondering what the effect of cutting these together will be. Thanks.

Bill Davis · October 2nd, 2007, 03:12 PM

Okay, you're saying that in shot 1 you're after dialog PLUS background sounds.
In shot 2 you're after the same background sounds WITHOUT the dialog.

SO the constant you're striving for is consistent BG sounds.

That means you have to look and listen with that goal in mind.

First analyzise where your background sounds are coming from and make sure they stay consistent relative to moving your camera. In other words, if the talent is in front of you, but the background crowd is behind your talent and you move your camera back - you're diminishing BOTH the talent and the background because you're moving your mic away from BOTH.

If the background is a room full of noisy people, and when you move your camera back, you're simply moving it to another position within a constant sound field, then you can expect the background level to remain constant as the dialog increases or decreases depending on your mic position.

Finally, and this is critical, if you want the BG to remain constant, you MUST avoid AGC (automatic gain control) which is built into many camcorders and can't be switched off in many consumer level cameras.

The reason is that when your dialog is present, the AGC will set itself for the dialog PLUS the background sounds - and when you go to record JUST the background audio, the AGC will INCREASE the recording volume, trying to keep the recording levels consistent.

So the proper way to record this is to set MANUAL AUDIO LEVELS with the dialog plus background - then making sure the background sound field is consistent - simply move further away from the source of the dialog to lower it's level relative to the constant background for your wide shot.

If you can't defeat AGC, don't totally freak, that just means you'll have to manually lower the BG track level in post - not all that hard to do.

Ben Hillier · October 3rd, 2007, 09:22 AM

Thanks for clarifying that Bill. So, Basically when shooting any scene that has mixture of dialogue and no dialogue parts with changes of position, its bascially best to set the manual audio level for the loudest event and then leave it. Changes of audio position will be quieter obviously but will give perspective (if dialogue isnt crucial). Cheers

October 1st, 2007, 11:06 AM	#1
Ben Hillier Regular Crew Join Date: Jun 2007 Location: Cali, Colombia Posts: 46	Audio Levels and Distance Situation: In a documentary context using on camera microphone - Shooting general scene of people up close then from a distance approx 20 meters. Catching inteligable words not important. Question? What are peoples general method of setting audio levels? Is it best just to leave them at level for close up, or is it best to ajust them for each shot? Or best auto gain in this situation? Just want to get some takes on that, thiking what would cut togther best ect. Cheers. Ben.

October 2nd, 2007, 02:19 PM	#4
Ben Hillier Regular Crew Join Date: Jun 2007 Location: Cali, Colombia Posts: 46	Thanks Thanks for your replies. I`m not hoping to get any inteligable vocies, just get atmos. Abviusly I do pick up atmos at 20 meters, just sounds real quite, and wondering what the effect of cutting these together will be. Thanks.

October 2nd, 2007, 03:12 PM	#5
Bill Davis Trustee Join Date: Jan 2004 Location: Scottsdale, AZ 85260 Posts: 1,538	Okay, you're saying that in shot 1 you're after dialog PLUS background sounds. In shot 2 you're after the same background sounds WITHOUT the dialog. SO the constant you're striving for is consistent BG sounds. That means you have to look and listen with that goal in mind. First analyzise where your background sounds are coming from and make sure they stay consistent relative to moving your camera. In other words, if the talent is in front of you, but the background crowd is behind your talent and you move your camera back - you're diminishing BOTH the talent and the background because you're moving your mic away from BOTH. If the background is a room full of noisy people, and when you move your camera back, you're simply moving it to another position within a constant sound field, then you can expect the background level to remain constant as the dialog increases or decreases depending on your mic position. Finally, and this is critical, if you want the BG to remain constant, you MUST avoid AGC (automatic gain control) which is built into many camcorders and can't be switched off in many consumer level cameras. The reason is that when your dialog is present, the AGC will set itself for the dialog PLUS the background sounds - and when you go to record JUST the background audio, the AGC will INCREASE the recording volume, trying to keep the recording levels consistent. So the proper way to record this is to set MANUAL AUDIO LEVELS with the dialog plus background - then making sure the background sound field is consistent - simply move further away from the source of the dialog to lower it's level relative to the constant background for your wide shot. If you can't defeat AGC, don't totally freak, that just means you'll have to manually lower the BG track level in post - not all that hard to do.

October 3rd, 2007, 09:22 AM	#6
Ben Hillier Regular Crew Join Date: Jun 2007 Location: Cali, Colombia Posts: 46	Thanks for clarifying that Bill. So, Basically when shooting any scene that has mixture of dialogue and no dialogue parts with changes of position, its bascially best to set the manual audio level for the loudest event and then leave it. Changes of audio position will be quieter obviously but will give perspective (if dialogue isnt crucial). Cheers