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Old February 28th, 2007, 03:38 PM   #1
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What do you set your limiter at?

This is an offshoot of a question I asked in another thread (thanks Ralph). Curious to know what limiter settings people use. We've been setting tone to -12dBFS on the camera and the mixer's limiter at +8dB leaving 4dB of overshoot before digital clipping. Anybody setting their limiter at +12dB (with tone at -12dBFS)? Do you ever clip digitally that way? It would be nice to pick up a little more dynamic range from what I'm reserving for overshoot. We use an SD302 mixer by the way.
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Old March 6th, 2007, 06:41 AM   #2
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Hey Marco,

I think you put some +'s in there when you meant to use -'s..

It depends on your limiter really.. Is it a true 'brick-wall' limiter? If so, I would set it at 0dB or maybe -1dB. If it's not, maybe give it 3 or 6 dB to work with, for any overs it may let through.

There's usually a 12dB difference between VU meters and peak meters, so make sure your meters are both showing the same information.

I would think you would want to match 0dB between both devices. Or is your mixer an analog board? Hmm, even if it IS analog, I would still match them to 0dB. Then set the limiter down a few dB, give or take a few more dB depending on how much of a brick-wall it offers. The nice thing about matching your meters is that you can watch the mixer and know for certain that when you get close to 0, the limiter will kick in, and that you've nearly consumed all of your headroom. Ideally, your limiter will barely kick in. Giving yourself more headroom before limiting will let you use close to 16 bits of headroom (the closer you get to 0, the more bits you use).

I would use a compressor before the limiter, to smooth out the peaks, and then use the limiter as a last resort for anything that does get through. That way you get a much smoother sound than just instant limiting when you get too close to it. Generally a limiter is a compressor set with an 8:1 ratio, give or take a little bit, depending on who you talk to.

Hope this helps!
-Eric
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Old March 6th, 2007, 07:18 AM   #3
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Originally Posted by Marco Leavitt View Post
This is an offshoot of a question I asked in another thread (thanks Ralph). Curious to know what limiter settings people use. We've been setting tone to -12dBFS on the camera and the mixer's limiter at +8dB leaving 4dB of overshoot before digital clipping. Anybody setting their limiter at +12dB (with tone at -12dBFS)? Do you ever clip digitally that way? It would be nice to pick up a little more dynamic range from what I'm reserving for overshoot. We use an SD302 mixer by the way.

What camera are you using? Or more importantly, what kind of metering does it have? Sound Devices has a chart on their tech support pages for their mixers with several cameras and for a digital camera with a PPM meter, they suggest sending 0dBVU tone from the mixer and setting it to -20dBFS on the camera, then setting the limiter in the mixer to +20dBVU (or mayba a hair less). The potential dynamic range of dramatic dialog makes the -12dBFS recording level a bit squashed. Music or interviews with less loudness variations might be recorded hotter.
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Old March 6th, 2007, 07:36 AM   #4
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What camera are you using? Or more importantly, what kind of metering does it have? Sound Devices has a chart on their tech support pages for their mixers with several cameras and for a digital camera with a PPM meter, they suggest sending 0dBVU tone from the mixer and setting it to -20dBFS on the camera, then setting the limiter in the mixer to +20dBVU (or mayba a hair less). The potential dynamic range of dramatic dialog makes the -12dBFS recording level a bit squashed. Music or interviews with less loudness variations might be recorded hotter.
I use an SD 302 and totally agree with your advice Steve. I usually have my limiter at +16dbfs but I calibrate to -20dbfs on the camera. At -12dbfs its kind of hard for me to maintain peaks properly when you're booming and mixing at the same time IMO. I don't keep my limiter all the way for safety sake, and I don't have to slam the limiter either with my levels. So far no complaints. :)
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Old March 6th, 2007, 07:47 AM   #5
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Steve — We do sound on a lot of people's projects, so this question is for pretty much every camera costing less than $10,000. They're all about the same aren't they — ranging from bad to worse audio wise. Yeah, I'd like to leave 20 dB of headroom, but from what I gather, it throws away too many bits.

Eric — The meter on the 302 goes up to 20 dB past 0. You can't set the limiter below zero. What you do is send a 1K tone to the camera (which registers as 0 on the mixer's meter), and adjust the gain on the camera to give you whatever headroom you want to leave, usually -12 dBFS. Then you set the limiter on the mixer to some level within that range. As I said, in my case we've been setting it at +8, leaving 4 dB of overshoot.

Another option, as Steve points out, is tone up at -20 dBFS and set the mixer's limiter anywhere from +16 to +20. My understanding has been that pretty much no camera in this price range is capable of leaving that much headroom without excessive hiss. Some people seem to be saying (and I won't claim to know, I've just been asking around) that it's not advisable on any 16 bit recording device.

My original question was about whether I really need to be leaving that 4 dB for overshoot. It would really help if I could set the limiter to +12, but I'm not convinced that the limiter will really prevent the signal from clipping digitally. I was hoping to find out how other people do it. It's a pretty common mixer.

Jeffrey — Thanks. That's the kind of information I'm looking for. Usually my partner mixes while I boom, so that's how we've been getting away with 12 dB of headroom. I can see how you'd have to leave 20 dB if you were booming and mixing at the same time, although I'd probably split the track if I was forced to record like that.
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Old March 6th, 2007, 07:56 AM   #6
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Steve is correct in his reply in my opinion, You'll find that on pretty much any shoot the audio department will be setting the camera to -20, it's pretty much a given in most circumstances.
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Old March 6th, 2007, 08:02 AM   #7
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Interesting. I assume we're talking about truly professional cameras here?
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Old March 6th, 2007, 08:43 AM   #8
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Steve is correct in his reply in my opinion, You'll find that on pretty much any shoot the audio department will be setting the camera to -20, it's pretty much a given in most circumstances.
Well I've seen many use -12dbfs cal.. particularly with the old school production sound mixers. From what I've seen, both cals are often used. In the end it's all really about preferences and having proper gain structure.
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Old March 6th, 2007, 08:54 AM   #9
 
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Originally Posted by Marco Leavitt View Post
Steve We do sound on a lot of people's projects, so this question is for pretty much every camera costing less than $10,000. They're all about the same aren't they ranging from bad to worse audio wise. Yeah, I'd like to leave 20 dB of headroom, but from what I gather, it throws away too many bits.

My understanding has been that pretty much no camera in this price range is capable of leaving that much headroom without excessive hiss. Some people seem to be saying (and I won't claim to know, I've just been asking around) that it's not advisable on any 16 bit recording device.

.
That's a pretty broad comment that others may be making, and I'd have to disagree. There are plenty of 16bit devices that are very capable of clean audio. To stay on point, the low cost (and the higher grade cams too) camcorders are noisy in the audio sections, which is why you'll virtually never find a mid to high level shoot recording audio to a cam, or they're double recording when they do record to the cam.
At the end of the day, you want to saturate *any* digital recording with as much audio as possible. You can be less picky with 20bit or 24bit, yet you'll still want hot signals. Noise is still audio whether it's 24 bit or 8 bit. It just happens to be more accurate noise in a 24bit stream. :-)
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Old March 6th, 2007, 10:16 AM   #10
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Deleted, sorry.

Last edited by Marco Leavitt; March 6th, 2007 at 10:22 AM. Reason: Spot already answered this
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Old March 6th, 2007, 11:15 AM   #11
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Spot, just to make sure I'm clear on this, do you think it's safe to tone up at -20 dBFS in this situation? I realize that you always want to record the hottest signal possible, but -12 dBFS just isn't working out for us much of the time. We try to do double system sound on our own shoots, but it's pretty much an impossible sell on the low budget filmmakers we work with.
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Old March 6th, 2007, 03:25 PM   #12
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Are you recording stereo sources? If not, why not run dual mono and set different gains on the 2 ins on the camera? Then your quiet stuff is recorded louder on one channel, and your loud stuff (which may clip) is recorded with more headroom on the other channel?
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Old March 6th, 2007, 03:32 PM   #13
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Actually, we do record with multiple mics and separate them out on different tracks fairly frequently. We have split the track on occasion as you describe though. It makes me a little nervous. I'm afraid post is going to screw it up. I don't really like doing it that way if I can help it.
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Old March 6th, 2007, 07:29 PM   #14
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Funny this should come up as i was just playing around with some of my different mixers limiters. Some can be set lower and still sound good and some should be set very high so you never really use them.
On my Shure FP-33's I set the limiter to +12DB which is about 6 DB lower than the factory preset +18DB which is basically off. If I am recording digitally to a camcorder I usually set tone at -20DB but run my peaks to -10 to -12. I leave the limiter in on the mixer most of the time but really don't want to hear it too much. I always check the digital camcorders meters with natural sound to get an idea how the camcorder handles the signal because tone often gives you a different response than the mixers meters would suggest. IE peaks on voices at -10DB on the mixer go to -12 or more on the camcorder.
On my Wendt X5 the limiter is set at the factory and it kicks in at +4DB according to the manufacturer but is more of a knee limit so it doesn't sound as harsh as a brick wall limiter. Same issues with tone compared to nat sound and levels. Some of it is VU vs peak and some of it is camcorders have different sensitivities to differrent mixers outputs. IE The Wendt X5 can drive on an XLH1 to a different level on the input than the Shure at factory settings (which can be adjusted post VU) or a Sound Devices.
The reason I usually go with -20 instead of -12 on the tone to a camcorder is so I can actually see some response on my mixer VU before I overrecord on the camcorder. Some camcorder models where so sensitive that -20 VU was too high a signal from the mixer. My feeling is you want to get everything into its sweet spot as far as S/N so the mixer should be sending a nice healthy signal and the camcorder should also be recording a nice healthy signal. If either are thin then you have a noisier recording
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Old March 6th, 2007, 11:11 PM   #15
 
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Originally Posted by Marco Leavitt View Post
Spot, just to make sure I'm clear on this, do you think it's safe to tone up at -20 dBFS in this situation? I realize that you always want to record the hottest signal possible, but -12 dBFS just isn't working out for us much of the time. We try to do double system sound on our own shoots, but it's pretty much an impossible sell on the low budget filmmakers we work with.
We print tone at -20dB as a reference point (I love this new ability on the Canon A1/G1 cams, BTW), however in the recording process, I frankly don't even look at averages. A -12dBFS average in recording *should* be fine, yet I'm always seeking the -3 peak in the recording process. If dealing with a very dynamic voice, I'll put a compressor before the cam audio if I'm recording to cam-only. Usually I've got at least a Microtrack if not an R4 or other external device.
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