help with audio meters

[michael L]

2 questions....

1. I haven't been able to get a definitive answer on what the marks on the meters correspond to. Is the embolden line in build 17 -12dBU? It is obviously different from the great whitepaper sounddevices released for earlier builds.

2. on a shoot yesterday and the meters would intermittently appear to clip. this was during normal dialog that we weren't pushing hard at all on the meters. periodically both meters would turn entirely red for a split second. the playback was fine with no clipping. we were backing up to a separate audio harddrive recorder but still...

any thoughts or similar experiences?

Michael

[Mike Burke]

2 questions....

1. I haven't been able to get a definitive answer on what the marks on the meters correspond to. Is the embolden line in build 17 -12dBU? It is obviously different from the great whitepaper sounddevices released for earlier builds.

2. on a shoot yesterday and the meters would intermittently appear to clip. this was during normal dialog that we weren't pushing hard at all on the meters. periodically both meters would turn entirely red for a split second. the playback was fine with no clipping. we were backing up to a separate audio harddrive recorder but still...

any thoughts or similar experiences?

Michael

The embolden line is meant to represent -20dbfs.
It sounds as though you're experiencing the same problem as we and a few others have.
Check out this thread. http://205.234.135.241/forum/showthread.php?t=26140

[Brian Ferguson]

If you send a real -20dBFS signal at line level from a Sound Devices Recorder (not mixer that is analog to analog) at line level it will hit the far right hash mark on the RED build 17 . I have also repeated these as standard signals in our lab.

The -20 1k tone will record on camera and playback in FCP. The RED VU scale right now looks a bit to heavily weighted to the right. Once you know where a true -20dBFS is (the far right mark) there is a +20 headroom from there.
Put it this way if you are not hitting the yellows on build 17 you are not hot enough. It might seem too far to the right on the scale but it is the proper place to be. Just saying.

[HD Hildebrand]

If you send a real -20dBFS signal at line level from a Sound Devices Recorder (not mixer that is analog to analog) at line level it will hit the far right hash mark on the RED build 17 .

What about from a mixer/analog to analog?

[Stuart English]

What about from a mixer/analog to analog?

Just make sure that a 1KHz tone also hits that right hash mark.

[Tom Visser]

There is an important distinction to make regarding dBU and dBFS. You cannot "send -20dBFS out of a mixer" at least not exactly. the dBFS scale is a digital scale that represents the mathematical clipping point of a digital signal. dBU is the electrical power output in relation to .7746v = 0dBU or dBV where 1v = 0dBV. dBU scale is more common in our field.

Where you can convert between voltage peak to peak, voltage RMS, dBU, and dBV, there is no way that you can convert to/from dBFS... because this depends entirely on how the device in question is calibrated. It could be calibrated correctly to the European standard, it could be calibrated correctly to the American standard, or it could be calibrated (or not calibrated) to its own standard. This is where the whole calibration process comes into play. It is not correct to assume that matching up equipment will show levels at the expected values... it is assumed that once you have tone, you then adjust the recorder / camera / submixer to the right input sensitivity to match the calibration target of your choice. RED makes it a bit more difficult since it does not have graduated input sensitivity adjustments, as it really should, or if they are brave enough to not provide such adjustment (only coarse adjustment in the form of a -10dB pad), then at least they should precalibrate it to match up with the Sound Devices 302, probably the most ubiquitous mixer out there.

It sounds like there is a defect in the board or installation process, though, by the accounts that some people are reporting where the input is overmodulating even though the RMS input levels are very low.

By the way, any mixer is capable of outputting tone, just because it doesn't have it built in, doesn't mean that you can't plug in a cheap external tone generator.

[Stuart English]

If you send a 0dBU (-20dBFS) line output signal from a Sound Devices Recorder / Mixer it will hit the far right hash mark on Build 17

The new beta Build 18 v3.6.4 has re-worked the audio meter sensitivity, see the Build 18 v3.6.4 Operations Guide for full details.

In summary with REV B audio hardware a 0dBu / - 20dBFS line input signal should align to the single Reference Level mark.

[George Hupka]

What about Build 17, and still waiting for my number to be called for the hardware upgrade? What does the hash mark correspond to there?