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Old July 17th, 2003, 02:10 PM   #1
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What'd I do wrong this time?

Okay, more audio problems. On a recent shoot, we had a scene where the characters talk normally for a while, and then begin to scream. Since the screaming was way louder than the normal volume speech, I adjusted the Canon XL1s' Audio 1 input level for the screaming, so it would go no higher than -6db. This of course made the non-screaming pretty low.

Anyway when I looked at the audio during the shoot, when they'd scream it go to -6dB and no higher, nowhere near zero. Listening to it afteward, and at home on my computer, the screaming parts are very overmodulated. I don't get it-- the audio meter said they were fine in camera, like I said, nowhere near zero.

I had my Sennheiser ME66 plugged into my MA100 - no mixer or compressor or anything fancy. Why'd it do this? I've had stuff go to -3 and almost to 0 dB and it sounded fine when I listened. Does screaming somehow make it distort when regular speech recorded at the same volume does not?
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Old July 17th, 2003, 02:39 PM   #2
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The screaming pegged the mic's diaphram, which caused it's signal to
distort no matter how loud or soft that (distorted) signal was recorded.
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Old July 17th, 2003, 02:59 PM   #3
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Jacques. . .explain?
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Old July 17th, 2003, 03:17 PM   #4
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You wouldnt use a ME66 (which is a shotgun mic) at any concert because it can get distorted so eaisly. At a concert you would either plug into the soundboard or use an oncamer mic or something equivlant to it. If Jaques wants to explain more it would be helpfun because I am not an expert by any standard.

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Old July 17th, 2003, 03:27 PM   #5
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All microphones have a maximum "SPL" (sound pressure level).
If that level is exceeded, you get nothing but horrible distortion, or
at least a big "crack" every time you exceed it.

Condensor microphones, like the ME66, are more sensitive
(have a lower SPL) than dynamic
mic like a sennheiser 421, which can record a gun shot without being "pegged"
"bottoming out", "fracking" or being forced to "full excursion".

By "pegged" I mean the diaphragm being forced by the passing sound wave(s)
to full excursion, meaning the diaphragm is no longer floating as it does
in normal operation. It is being held at the end of its travel limit . . . pegged.

Most high end condenser mics have a pad that helps avoid this problem.

I am not sure of the circumstances of this shoot, so this is my best guess.
I have also recorded distortion on my XL1 through the MA-100 adapter
when receiving a +4dBu line level signal, even though the meters said
all was well and the settings were for line level (which is -10dBu btw).
Could it be that?
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Old July 17th, 2003, 03:57 PM   #6
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It was set at either mic or mic ATT - I think Mic. So it's the microphones limitations. . .not necessarily anything I did? Does this proximity matter? We were in a bedroom, maybe 12' by 12' --very echoey environment. If I were taping a screaming crowd in a larger area, from like 10 feet away. . .would there be a difference? Maybe I should listen to the headphones next time, instead of letting someone else.

What if I had turned the input way down, so that even though on the meters it looked too low, at least to my ears it would sound clear?
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Old July 17th, 2003, 04:17 PM   #7
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A single human voice can be incredibly loud. Add a few more humans yelling,
and a tiny room with hard acoustics . . . that could do it.

Direct the actors not to yell so loud. Keep the intensity, but drop the volume.
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Old July 17th, 2003, 05:14 PM   #8
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That would be the director's job. . .I was not he. And, I did tell them that.
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Old July 17th, 2003, 06:22 PM   #9
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Yeah, and as the TD, you probably still took the hit. ;)

That's what sucks about this side of the business.
If the audio, the lighting, the framing, the exposure,
etc., etc., etc. is _all perfect_ . . . no one notices.
Any error and it's YOUR fault . . . argh!

In any case, tomorrow is another day :)

Jacques "long day in the studio and emailing DVINFO" Mersereau

PS Believe me, I am not trying to blame anyone, and I know it is a lot harder
to get it all right than to miss once.
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Old July 18th, 2003, 06:06 AM   #10
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Josh...

It could be that the mic picked up the screaming OK but your audio circuit got overloaded. It's happened to me before where the signal sounded OK on the headphones but was distorted on playback. Somewhere between the headphones and the tape something's getting overloaded.

Someone on this board mentioned a trick he uses for sounds with extreme dynamic range. He splits the source between the two tracks. One is set normally. The other set to handle very loud transients. He then selects the best part of either track in post production.
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Old July 18th, 2003, 12:29 PM   #11
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Uh. . .how would I do that? I've been using a y splitter to make my mono shotgun signal mono, plugging it into the splitter and then one end of the splitter into each input of the MA100
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Old July 19th, 2003, 02:06 AM   #12
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Since you're splitting it to seperate channels you can use the "balance" control to set the recording level higher on one channel than the other. Unlike some broadcast cameras which have seperate level controls for each channel, the XL1 has a balance control like that on a stereo system.

Make sure your audio controls are set on manual or the widely varying sound levels will wreak havoc with your audio.
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Old July 19th, 2003, 10:25 AM   #13
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If you take a closer look at the post, Josh said:

>Anyway when I looked at the audio during the shoot,
>when they'd scream it go to -6dB and no higher, nowhere near zero.
>Listening to it afteward, and at home on my computer,
>the screaming parts are very overmodulated. I don't get it--
>the audio meter said they were fine in camera, like I said, nowhere near >zero.

If the signal was not incorrectly recorded at the camera, it would
appear that the signal was *already distorted* when recorded.
Distortion was recorded, not _created_ by the camera's gain control.

Splitting a distorted signal and recording it to two channels with different
input levels won't change a thing, except recording loud distortion
and quiet distortion.

I stand by my theory that the mic itself was overloaded by the screaming.
I find it interesting that through the headphones, the sound
was reported as good, but when you're in a room with people screaming,
who can really say with that kind of bleed in the phones.

That's why recording studios have sound proof control rooms.
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Old July 19th, 2003, 10:39 AM   #14
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Yeah, well, like I said, I personally was not listening to the phones, and they're not the best phones anyway--really surprising given the $20 price tag.
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Old July 22nd, 2003, 05:48 AM   #15
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The ME66 has a relatively high output level, you may have been overloading the first stagge of the XL1 mic input preamps (before the level controls and meters) if using the MIC setting.

As I recall the ME66 nominal output is around -28 dBV at 1 Pa SPL, which is a reasonable match for the XL1 MIC ATT input rating (-35 dBV), and substantialy above the nominal -55 dBV rating of the MIC setting. It may be that with the shouting the XL1 inputs were overloaded. Note that the MA100 adds about 6 dB of gain to the system too. The ME66 is also rated for 126 dB max SLP (1% distortion) so I doubt if the mic itself was overloaded by human voices several feet away.

MIC ATT would probably have been a better setting.
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