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Old January 1st, 2004, 09:20 PM   #1
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What's Wrong With My Audio?

I shot a reception yesterday. I used a Rode NT4
mic. The DJ's music was pretty loud, but not that
loud. I rode the levels manually; kept it peaking
around -9 dB. All the audio turned out muffled.
It sounds like music playing on a blown speaker.
At the reception that I shot previous to this this one,
I had this same muffled sound happen for about a minute when I was near the DJ's speakers, but as I moved away from the speaker the audio came back to
normal over a few minutes time.
What's going on here????
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Old January 2nd, 2004, 12:01 AM   #2
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It is possible to peak the microphone or the preamps of your camera, before the volume controls. So that your levels "look" fine, but your audio is distorted. You should hear this distortion on the headphone outs of your camera while your recording though.
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Old January 2nd, 2004, 01:51 AM   #3
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You're also at the mercy of some DJ's sound system. Although i'ver been in that sirtuation very few times, I can't help but think his archaic definition of a sound system is somehow at fault.

Without fully understanding the physics, i had a problem with a DJ's output interferring with my audio. I used my mic and my mixer and gave him a feed and also fed my camera, everything was great. I realize this is not always possible but it points to a problem that you may have little comtrol over.
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Old January 2nd, 2004, 01:54 AM   #4
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Martin,
Yes, I was monitoring with Sony 7506, and it sounded
very distorted the whole time, but at the time I figured the headphones couldn't hang in, seeing as the cam levels were
well below clipping. What's going on? Is my
Rode blown? [Rode NT4 is rated for high SPL (~134).]
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Old January 2nd, 2004, 02:01 AM   #5
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Beas,
No, it had nothing to do with the DJ.
Yes, his system wasn't great. But this is a problem
with me. Very muffled. Wanna hear? I'll
pass along a clip if you think it might help.
I'm clueless.
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Old January 2nd, 2004, 02:17 AM   #6
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If the mic is rated pretty high, then I would look to the camera pre-amps. Which camera or input device are you using?

I know with the pd150, and a hot mic it was often necessary to use the mic attenuator, which I believe is a 20db pad. But with any camcorder, your margin of error between the best level and blown is pretty small. Often 20db, is too much of a drop and you introduce noise by gaining up the camera.
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Old January 2nd, 2004, 10:21 AM   #7
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I'll bet you two (2) donuts that it was air pressure distorting the recording.

There are a handfull of things that could cause this foul air. (insert joke here)... For one, I'd consider that mic a studio mic rather then a "busy location mic"... If you'd have had it in a Zepp w/ Furry I'll bet you wouldn't have had the offending "muffle"... even a Zepp may have done it.

What happens in a busy area of movement is a lot of shifting air currents... and with a very sensitive mic you can have a steady stream of air which keeps the diaphragm under steady pressure. Then the mic fights to "float" the diaphragm as it usually would. Result? Muffled sound.

Common causes of this are: 1) Lot's of human movement causing air currents. 2) An ac/heating system which is flushing an area with air movement, EVEN if you don't perceive air movement. 3) If the mic is on a boom or camera, then FORGET getting decent sound when either is NOT locked down... unless you have the Zepp and Furry.

I would expect the nt4 to be far more delicate to these factors then an AT4073a... When I bought a Rode, I figured it would be a stay at home mic.

Finally let me just say that perhaps I'm wrong about all this, but I doubt it.
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Old January 2nd, 2004, 03:54 PM   #8
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Dave,
If you're using a PD150, try using MICATT and set your levels to about -20 with a peak at about -12db.
This is how I've been running mine and they seem to work fine that way. At worst audio is slightly low and can be raised in post without doing harm.
I know Mike and others use AGC on theirs but it's not worked for me for whatever reason.
Maybe this will help, maybe not.
Don
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Old January 2nd, 2004, 04:28 PM   #9
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So is it possible to overload the preamps without
having the dancing meters pegged? What
would loud music sound like through
overloaded PD preamps?
And is the PD attenuator *before* or *after* the
preamps in the chain?
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Old January 2nd, 2004, 05:03 PM   #10
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I overloaded one time and the meters stopped dancing and pegged didn't move at all and the music was very loud and distorted in the headphones.
I THINK the attenuator is after the amp but I could be wrong.
Play around a little and if you search thru this forum and the audio forum I think you'll find a lot of info. I know Mike R. and I as well as a few other good folk have posted on the 150's audio. You might even try AGC, who knows, it might work for you, it works for Mike.
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Old January 2nd, 2004, 08:02 PM   #11
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You very likely overloaded the preamp input. One can apparently overload preamps and not cause an high level. I've had this happen twice to me recently. Both times I could not hear the distortion. Happened on a ME2 connected to the Senn wireless and on my studio microphone. In both cases I didn't have the attenuator in the circuit and should have. But the senn microphone was on the back of the actors shirt collar, he just had a very deep voice. The studio micorphone did it on-stage at a theatre with the same person I normally use for voice-over work. He apparently decided he was on-stage and therefore should use a stage voice.

My staggered gain settings on the PD150 made no difference in both cases. The channel on auto gain was as distorted as the channel on low manual gain.

From now on, I'm going to run the attenuator on on the camera and take the lower levels as they come.

If you can hear distortion on 7506's, then there is distortion in your audio. The headphones will handle more than you can shove at them from the camera.
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Old January 2nd, 2004, 08:49 PM   #12
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So with a variable in-line attenuater, do you just keep
stepping up the attenuation until the distortion goes
away?
I just checked my Rode mic and it's fine. It must
be fairly sensitive because I only had some
music playing at medium volume and at the
same gain (2/3 of max) as I used at the reception, the
levels were approaching 0 dB. The DJ's music
was a lot higher than what I did with my
speakers.
Mike, do you happen to remember what levels
you were showing when you got the distortion?
Does anyone think the situation would've been
different if I had used AGC?
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Old January 19th, 2004, 06:55 AM   #13
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Don,
I've done some experimenting and have found out
that the attenuator is *before* the preamp input.
I recorded some loud music at the "MIC" position,
peaking at -3 and -12 with a sensitive mic (manual
gain at 30% and 20%). I got distorition both times.
I then recorded the same music at "MIC ATT" (which
I believe is a 20 dB pad) with manual gain set to
60% of max, which yielded -3 dB peaking. Voila, no
distortion.
The in-built 20 dB pad does really cut the
incoming signal. I ordered 10 dB in-line attenuators.
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Old January 19th, 2004, 08:37 AM   #14
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Dave,
Thanks for the update.
Shows what I know, I use the ATT position alot at receptions and of course it works great but HEY! I had a 50/50 chance right? Before---After.

Don
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Old January 19th, 2004, 10:32 AM   #15
 
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In quickly looking at this thread, I didn't see anyone mention the AGC? Automatic Gain Control is found on most cameras, consumer and pro-sumer, and the description sounds just like AGC. Clean sound, with muffled instances due to the AGC clamping down. Either switching off AGC or using a controlling device like a Beachtek will generally allow for this to be avoided. Unfortunately, most cams don't pass the headphone signal after AGC processing, so you don't hear that it's been processed. If they did pass the post-AGC signal, then you'd most likely experience latency.
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