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Old August 12th, 2010, 04:46 PM   #1
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Calibrating mixer with cam

So I'm trying to calibrate to my mixer and cam. I've been fiddling with it but I have a question. First I should explain since I have an older version Promix 3 it doesn't have reference tone. I have therefore connected my old Shure FP-31 and have been setting levels using its tone like so:

Shure: turn ref tone on, increase master until vu meter reads 0db. Line-level output to Promix.

Promix: Line-level input. Increase input gain until LED meter reads 0db (first amber light). Line-level out both channels to cam.

Cam: Line-level input both channels. Audio reference set to -12db.

When I crank the input pots on the camera all the way, the audio meter peaks right before I reach the red (just below 0db). So my question: am I doing this correctly? I could get a TonePlug to replace the Shure, but it's essentially feeding me the same level tone into the Promix right? Should I have to be turning the camera inputs all the way up?
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Old August 12th, 2010, 05:13 PM   #2
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The original Promix 3 had a low line-level out, around 0db, to work with the DVX-100. It won't be hot enough for most cameras.
You might need to use mic-level out to mic-level on the camera, that's what I have done before.
If you push the promix too hard trying to get more line-level output it will distort.
And you shouldn't push the camera controls that high generally.
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Old August 13th, 2010, 03:26 AM   #3
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Gain structure is always an issue, and people have different ways of managing it - but the problem gets made worse by some kit that appears to have different 'interpretations' of a standard. The aim is to maintain signal to noise throughout the chain, so in this case, I'd experiment with sending the camera tone at various levels, then sticking the file into an audio editor and identifying the exact level that starts to distort. If you then work backwards, you can do similar things with the other kit and find the optimum settings on each one to produce the highest, but cleanest output settings. When cascading kit in this way, the other thing to take into account is how noisy the electronics are. If one item is low level out, and the item connected to it has noisy pre-amps then this is going to be difficult.
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Old August 13th, 2010, 10:25 AM   #4
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Christopher,

I'm not completely sure I understand the last part of what you wrote. You say that you set the audio reference to -12, but then talk about it peaking just below 0 when you turn the gain all the way up. Why would you turn the gain all the way up? Your reading on the two mixers at 0 is fine. Remember that those are analog devices and 0 dB is your reference point with peaks o.k. up to maybe +6dB or even a little higher. Your camcorder is using a digital scale, where 0 is the TOP end of where you want to be. Anything over 0 is distorted. So the level you would want that to show on your camcorder is usually around -16. You have apparently chosen -12. That gives you 12dB of head room, which should be fine if monitored.

Please ignore if I haven't had enough coffee to understand your question. Have fun!

Rob
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Old August 13th, 2010, 12:57 PM   #5
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Thanks for the input guys.

Jay: I'm pretty sure line-level (0db) is hotter than mic level (usually -50db). The only way I've been able to increase the volume coming into the camera is to switch the output on the Promix to mic, leaving the input on the camera on line-level. When I do this the audio meters on the camera peak when I turn the gain pots up to around 2...

Rob: The Shure is an analog mixer, the Promix is digital. The GY-HD100 has a setting in the audio menu to record to tape at -12db or -20db. I chose -12 to get the loudest sound possible to see where my ceiling was. My concern is that if I have to turn the camera gain all the way up to match the LED reading on the Promix I'll be getting very weak sound once I bring the camera gain back down to a good medium level.
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Old August 13th, 2010, 01:51 PM   #6
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What I said was since the lower-than-standard line-level output of the Promix is often not hot enough to get a full signal into a camera that needs full +4db line-level input, you can instead use the Mic-Level out of the mixer and also set your camera to Mic-Level. This will often be a better match.

Either you've just typed your last post backwards or something is wrong with your camera or mixer. What you've described in the last post is the opposite of what should be happening.

The following is what should be happening:
Line-level out from the Promix will often not be hot enough to supply full Line-level into the camera.
Mic-level out from the Promix into Mic-level on the camera should be a close match.
Mic-level out from the Promix into Line-level on the camera would give almost no signal at all.
Line-level out from the Promix into Mic-level on the camera should be a huge overload and you shouldn't do it that way.

The Promix is an analog mixer.

The reference level in the camera menu usually just affects where the meters show when you're reaching that reference level. For example when the metering turns from amber to red, or when a specific mark shows up in the metering, depending on the camera model. I don't have experience with that particular JVC camera though.

You need to find settings on the mixer and camera so that a "0" indication on the mixer reaches your reference level on the camera, without having to turn your camera inputs all the way up, so your original question is valid. It's just a question now of experimenting with settings.
Are there other camera menu settings other than the reference level? Such as a sensitivity setting for the inputs themselves?
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Old August 13th, 2010, 03:00 PM   #7
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Jay,

You're right, I misspoke (twice!) the Promix is analog and I did reverse the input/output settings. Unfortunately I don't think there are any other menu settings to control the audio inputs on the HD-100.

So I have mic-level out of the Promix and mic-level into the camera set to -12db. The first set of amber lights are lit on the mixer, and the camera hits the first set of amber (yellow) lights when the gain hits around 7. I think the automatic limiters on the Promix outputs keep the signal from clipping in the camera unless I completely overload the signal by going line-out to mic-in.

This is closer to what I should be shooting for, right?

I appreciate everyone's patience with me as I'm still learning. Thanks!
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Old August 16th, 2010, 11:52 AM   #8
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Bump

Just looking for confirmation before I start shooting my next project. Thanks!
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Old August 17th, 2010, 12:25 PM   #9
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Without having my Promix3 in hand or having familiarity with your camera, that last description sounds like a much better situation than what was happening originally.
As always it's very important to monitor the sound quality with good headphones connected to the camera. The meters by themselves only tell part of the story and actually listening at the camera during recording is critically important.
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Old August 17th, 2010, 04:28 PM   #10
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I never show up without my 7506s!

Thanks again for your input Jay.
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Old August 23rd, 2010, 04:24 PM   #11
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This might help:

Broadcast Audio Operating Levels for Sound Engineers

An old document from a few years ago but now used by Avid I'm told ;)
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