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  • Hey all, just changed over the backend after 15 years I figured time to give it a bit of an update, its probably gonna be a bit weird for most of you and i am sure there is a few bugs to work out but it should kinda work the same as before... hopefully :)

Audio Levels - Fine When Recording / But Low Levels in QT-FCP

Audio Levels

Audio Levels

Just re-checked the level of a Ch 1 and Ch 2 line level recording of 0dB / -20dBFS tone from a Sound Devices 302.

This aligns to the solid white Reference Level mark of the RED ONE audio meter (see attached JPEG)

In FCP, I see -18 indicating for each track when metered as an individual channel of a stereo pair (and -12 if I meter as a stereo pair and / or I change the metering to dual channel mono)

And what does that 788 reference tone recording show in FCP?
 

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Frankly I think it'd be a good idea to talk to Sound Devices direct - they did a break down of interfacing their mixers with Red back when the audio board was not as good. Maybe they'll have a look again with some recommendations if Red ask them?
 
Audio Levels

Audio Levels

Is that a comment for us (RED)... ?

If so, I would love to get the feedback on the issue being discussed first.

Not convinced that there is a technical issue here to solved to be honest.
 
Hi Stuart. Yes it was just a suggestion. Feedback is of course useful, except that I've often found that audio interfacing is surprisingly open to a lot of different opinions of what are "correct" or "standard" levels, and even more so when international. Sound Devices obviously already know quite a bit about audio and how their equipment is used, and they are very common on shoots these days.
 
Audio Levels

Audio Levels

I've often found that audio interfacing is surprisingly open to a lot of different opinions of what are "correct" or "standard" levels, and even more so when international.
Click to expand...

That's for sure :wink5: and its also a discussion not helped by dB being both a relative scale and if people drop the "u", or "VU" or "FS" qualifiers...

Irrespective of the absolute level of the signal recorded though, I think there is something else operationally going on here - for example, are people taking the Reference Level to be the peak level that recordings should be made at, hence the average record level is well below that point; or as an indication of the average record level?
 
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Hi Stuart. . .

A clip is a clip is a clip. If it hits red, I'm assuming we've run out of bits and we're into clipping. And that doesn't sound particularly pretty with a digital device (although I like a lot of value clipping in my guitar amp!). Thus, since there is very little headroom in the RED audio circuit, we HAVE to use the meters as peak indicators, as any hot spots in the audio will result in "clippage" in the "soundage."

But none of this changes the fact that a lot of us are getting ridiculously low audio levels in FCP when importing our RED files. I'll try to do an experiment later this week once I have my grades turned in.

Thanks.

Stephen
 
Audio Levels

Audio Levels

A clip is a clip is a clip. If it hits red, I'm assuming we've run out of bits and we're into clipping.......we HAVE to use the meters as peak indicators, as any hot spots in the audio will result in "clippage" in the "soundage."

But none of this changes the fact that a lot of us are getting ridiculously low audio levels in FCP when importing our RED files. I'll try to do an experiment later this week once I have my grades turned in.
Click to expand...


So are you saying that you ARE using the 0dB / - 20dBFS witness mark as the maximum allowable signal level for your audio recordings?
 
SD302 > RED > Pr+FCP > ProTools Test

SD302 > RED > Pr+FCP > ProTools Test

After reading all about these issues you guys are having with audio and the newer builds I decided to do a comprehensive level test.
There are two actual tests, one is 0dBu and the other is Clip.
When an audio operator goes to test the levels, he sends tone (1KHz) at 0dBu/-20dBfs to camera.
Our Sound Devices 302 tone lined up perfect with the "Witness Mark" as described by RED.
When he sees this 1Khz tone, he knows he should have +12dBu and +20dBfs headroom above tone.
In the real world, I've found that +18dBfs is the ceiling in most applications, this is no exception with the RED!
Thats the basics of how this works.

RED Audio Test with Build 20.1.3, new audio module.

From the RED manual:
"Peak Level meter with 0dBu (-20dBFS) Witness Mark in the Graphical User Interface."
"Peak Level meter range is –34dBu to +20dBu (-54dBFS to 0dBFS) and provides clip indication."

THE TESTS
All results were metered as individual channels, even though I ran 2 channels for redundancy.
In Premiere, I thought we were getting varied results but when both tracks are panned center, the overall level goes up +3dB. Pan L+R to fix.

0dBu TEST
Defined as internally generating tone from a Sound Devices 302 mixer sent at 0dBu/-20dBfs to the RED. 2 Channels, Line level.

RESULTS:
RED 20.1.3 = -20dBfs/0dBu Right on the witness mark.
Premiere 4.1.0 = -12dBfs
Final Cut Pro 7 = -12dBfs
ProTools 8 (OMF from Pr) = -11.67dBfs
ProTools 8 (OMF from Fcp) = -11.67dBfs



CLIP TEST
Defined as running a tone generator into a Sound Devices 302 and gaining it up on the mixer until just beneath clip on the RED (+18dBu). 2 Channels, Line level, Limiter turned off.

RESULTS:
RED 20.1.3 = Just below clip
Premiere 4.1.0 = Just below clip
Final Cut Pro 7 = Just below clip
ProTools 8 (OMF from Pr) = Just below clip
ProTools 8 (OMF from Fcp) = Just below clip

CONCLUSION
Our audio is just fine. What RED & Sound Devices call -20dBfs is actually recognized as -12dBfs in all the post production software tested here.
I'll be honest, I never totally understood where -20dBfs came from as a calibration level for tone.
Tape saturation (The analog equivalent of clipping) occurs at +12dBu, so why not have tone at -12dBfs?
I can only speculate this is somehow tied into broadcast safety leveling but as long as you know how to navigate through it, I guess it doesn't much matter!

I hope this has verified that issues with FCP are not happening to everyone. Even though we have FCP7, this is how it worked under 6 as well. We've never had issues with levels once figured out.

PS - If anyone has any answers on why -20dBfs is used for tone, I'd love to hear it.
 
James Brundige said:
FYI. Wendt X3 mixer. 0dB tone from the mixer just lights the yellow in the camera.

In FCP, reads out as -14, -26 below unity.
Click to expand...

What do you mean -26 below unity? Seems like confusion between digital and analog meters. The FCP meter clips at 0 on the digital scale.

From Wikipedia
"0 dBFS is assigned to the maximum possible level.[1] A signal that reaches 50% of the maximum level would peak at -6 dBFS, for instance. All peak measurements will be negative numbers."
 
Where should the levels on the camera be when sending 1khz from the mixer to the camera? when I do it I have a little bit of yellow on the line, is that right or it should be all green? I am having the lines at 0 dbs.

Its a bit confusing for me so...
Is it correct -20dbfs (744t) = 0db (red camera) = 0dbu (mixer)

Thanks
 
Levels

Levels

Is it correct -20dbfs (744t) = 0db (red camera) = 0dbu (mixer)
Click to expand...

That is correct, at that level the RED audio meter should be all green and align to the witness mark.

The above assumes Build 18 or 20 and Rev B audio board.
 
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Well, I have got the input leves on the red one set to line at 0dbs but the channel 1 is way below that marked line...its just about the beginning of the green line, while channel 2 is just at the marked line...

Any ideas or suggestions of things to check?

Obviously I am sending audio tone 1khz from the 442 to the camera...

Thanks
Vicente
 
vicente villaescusa said:
Well, I have got the input leves on the red one set to line at 0dbs but the channel 1 is way below that marked line...its just about the beginning of the green line, while channel 2 is just at the marked line...

Any ideas or suggestions of things to check?

Obviously I am sending audio tone 1khz from the 442 to the camera...

Thanks
Vicente
Click to expand...

Do you mean you are seeing just one segment of green on the scale?
Have you tried other channels? 3&4 as well? What build are you on?
 
The Red meters are very dicey. If you set tone to touch the yellow, you will have only 6 dB above that until you distort. Recording at a safe level, your audio will need to be significantly boosted in FCP. Because it is digital, the noise floor makes this boost possible, though it is not ideal.
 
Audio Input Levels

Audio Input Levels

Yes, but you shouldn't be setting the tone to touch yellow....

You should be setting tone to touch the 0dBu / -20dBFS witness mark - as the Operations Manual says.

Then you will have an operating headroom of approximately +18dB above tone, and +20dB before digital clip.
 
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