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Old March 31st, 2008, 02:28 AM   #1
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Setting reference level on camera

Hi,
Hopefully this question only needs a really simple reply.
I have a shure fp24 and sony dsr-250 camera. When outputting the 1khz reference levels to the camera, should I adjust the camera gain so that the levels hit 0db, or should they be hitting -12/-20db?

I don't really understand if the 1khz signal is a maximum being output from the mixer, meaning that no clipping can occur to the camera audio as long as the levels are ok on the mixer.

Thanks
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Old March 31st, 2008, 02:52 AM   #2
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Mixer reference tone is at the old analog 0 dBVU point, which is at -20 dBFS digital domain you camera uses. So you should set the tone at -20 dB on the camera. The reference tone is 20 dB below the maximum level mixer can put out.

With this setup, if the mixer meters (peak reading mode) do not hit +20 dBVU, the audio on the camera can not clip. If you use the limiter on the mixer and the levels are set sensibly (on the mixer, no setting on camera anymore), it is impossible to clip the audio while getting nice high levels.
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Old March 31st, 2008, 08:58 AM   #3
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what about when the camera doesn't display the actual numbers ( -20, -12) but rather just two vertical lines. Do those lines represent -20 and -12? Thanks
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Old March 31st, 2008, 10:58 AM   #4
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Yes...

Usually -20dBFS is marked with vertical line or change of color. Or could be -12.

Easy test: set up mixer-camera connection with the test tone at assumed -20dBFS point on cam. Make loud noises with levels approaching +20 dBVU on the mixer, does the level get to almost 0 dBFS on camera? If yes, Bob's your uncle. If camera clips, then the marker is at -12dBFS.
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Old March 31st, 2008, 12:42 PM   #5
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I reference to -12dBfs in camera (not on delivery masters) to get a little more signal to noise ratio. However, I've "lost" the extra 8dB of "insurance" headroom by doing it. So this method works fine for predictable sound levels (a seated interview) but I wouldn't recommend it for run and gun news stuff surrounding an industrial fire, for example.
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Old March 31st, 2008, 01:13 PM   #6
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That's correct Shaun. I'd be white knuckled if I set tone to -12 on a digital camera, even with a good limiter in the mixer.

People's voices vary from person to person quite a bit. Some have low Peak to RMS voices. In others the Peaks are WAY higher. I'm not talking about how loud they speak. I'm talking about the way the meter indicates the distance between their RMS level and Peak level during normal speech.

I set my tone to -20 on the camera and run my mixer (with limiter set to +16) so that peaks occasionally light the limiter light. That usually results in camera meters that peaks about -6dB, with room for the occasional quick burst, clap, cackle or other quick noise that will sneak through my mixer's limiter.

Regards,

Ty Ford
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Old March 31st, 2008, 11:32 PM   #7
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Thanks. Interesting reading.

When I try using the same shure fp24 with my marantz pmd670 solid state recorder, the audio clips really badly on the recorder even with mild gain on the mixer.

I set the levels on the recorder (turn the the recorder's gain wheel down to "1") so that reference tone from the mixer hits about -20db on the recorder's meters. But when recording, as soon as the sound goes anywhere near 0db on the mixer's meters, the sound starts clipping on the recorder. This means that I have to keep the gain on the mixer down to about 1 or 2 as well.

However, when listening through the mixer's microphone socket, I can up the gain and talk into the mic so that the levels go way past 0db and never hear even the slightest clipping.
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Old April 1st, 2008, 03:11 AM   #8
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Brian,

Sounds like a classic levels mismatch. Are you sure you aren't feeding a line level output signal into a mic level input?

Also I don't know these particular machines. Does the target machine (the Marantz) have AGC circuits? (auto gain control) If so, you MUST get these turned off (if it's even possible) or you'll suffer major problems recording anything well.

Good luck.

After I posted this I looked at the manuals for each online and sure enough, they indicate that the FP24 is only capable of putting out a Line Level output via XLR and the PDM 670 has no pads on the mic inputs. You'll have to either use XLR to RCA adaptors to feed the unbalanced line inputs on the 670 or buy a pair of 30db XLR inline pads to bring your line level output down to the mic level input on the 670.

Last edited by Bill Davis; April 1st, 2008 at 03:23 AM. Reason: Did more research.
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Old April 1st, 2008, 03:14 AM   #9
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Hey All.

Doesn't Marantz PMD670 VU meter works @ old analog dBVU scale instead new dBFS? Just a dummy question.

Best

Ari
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Old April 1st, 2008, 07:06 AM   #10
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Quote:
Originally Posted by Brian Parker View Post
However, when listening through the mixer's microphone socket, I can up the gain and talk into the mic so that the levels go way past 0db and never hear even the slightest clipping.
How do you listen through a mic jack?

Regards,

Ty Ford
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Old April 1st, 2008, 10:35 AM   #11
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Sounds like Mismatch

These are classic symptoms of the Mixer outputting Line Level and the Recorder set to accept Mic Level. There is a 30-40dB difference between the two so the "ramp up" effect of gain would be substantial, even changing the input SPL slightly.
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Old April 1st, 2008, 09:05 PM   #12
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Thanks for the info Bill/Shaun. That's great (well not great, because now I need to go and buy pads, but I'm grateful that you checked the manuals for me).

I just did a search for 30db inline pads. Would something like this be right:
http://www.fullcompass.com/product/299976.html

So apart from the obvious logic that the input/output levels on each device should be of the same kind, is their any other disadvantage to mixing them like I am? I guess that lack of finetuning (slight adjustments to gain on the mixer have massive effects on the recorder) could be a problem. But on the other hand, I can keep the recorder's gain much much lower when using mic level input on line level output, thereby keeping the noise from the recorder's preamp to a minimum.


Ty, Sorry typo. I meant headphones jack.

Thanks all for enlightening me.
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Old April 2nd, 2008, 03:35 AM   #13
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Brian,

Those will work just fine.

Pads in the range from 30-50db will be very workable for this. At 30db, you'll have an inherently stronger signal passing through which would be good for recording quiet stuff. On the other hand, if you're mostly recording top fuel dragsters - you'd want more pad so you don't overdrive the mic inputs.

But all of them will get you in a range you can work with.

Good luck.
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Old April 2nd, 2008, 04:58 AM   #14
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Originally Posted by Bill Davis View Post
Brian,

Those will work just fine.

Pads in the range from 30-50db will be very workable for this. At 30db, you'll have an inherently stronger signal passing through which would be good for recording quiet stuff. On the other hand, if you're mostly recording top fuel dragsters - you'd want more pad so you don't overdrive the mic inputs.

But all of them will get you in a range you can work with.

Good luck.
Just a note - if the SPL is THAT loud one might want to use a mic with a builtin pad or a modular mic like the Oktava or Schoeps that has a screw-on pad available to insert between the capsule and the mic's own electronics. Extreme SPL can overload inside the mic before an inline pad on the mixer's inputs would have a chance to do anything about it.
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Old April 2nd, 2008, 11:43 AM   #15
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But on the other hand, I can keep the recorder's gain much much lower when using mic level input on line level output, thereby keeping the noise from the recorder's preamp to a minimum..
Sort of... in a perfect world, you want to run your recorder at Unity gain (usually about 70% of the way up) which is where the pre-amps neither boost nor cut the gain. This allows for the greatest dynamic range (signal to noise ratio) and the cleanest signal path. Having said that, this is the real world. Do what you need to make the application work for you. If it's quiet enough for your clients, it's quiet enough.
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