Mixer Level Meter Readings Above 0 dB

rtbond wrote on 1/5/2004, 7:15 AM

Hello,

This is a technical curiousity from a digital audio and Vegas newbie.

I understand from a practical perspective that clipping occurs at 0 dBFS (as you have run out of bits to represent higher signal levels), so you want to keep your audio peaks below 0 dBFS.

What exactly does the Mixer Level Meter in Vegas doing when it reports levels **above** 0 dB, if 0 dB equates to the maximum digital signal level (as I current understand it)? For example, what does a level reading of (positive) 0.7 dB really mean?

Does the Mixer Level Meter display digital audio levels in dB Full Scale (dBFS)?

Assuming yes, then how is it posible to have a reading above full scale? I thought full scale meant the largest magitude voltage sample that could represented in 16 bits. If so, then how is the meter able to determine ("see") magntudes above the maximum that can be represented? I've seen Vegas display audio levels above 0 dB on some captured live concert recordings I've made using a digital camcorder (with the external mic whose levels were set too high)

Yes, a bit of a silly question, but I'm trying to piece together my understanding of Vegas and digital audio. I'm clearly missing something.

Thanks!

--Rob

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Comments

PipelineAudio wrote on 1/7/2004, 10:50 AM

its not just that. The reconstruction process of the waveform itself can cause overs that are not detected as such check that link I posted a few back. I think it is part of an advertisement, but the theory is sound

RiRo wrote on 1/9/2004, 7:22 AM

One of the radio stations I do voiceovers for uses Sony 4-track minidisc machines for production, and it suffers with this exact problem. The led meters are not fast enough to accurately track all the fast peaks (snare, sibilance) and when it hits 0 it makes an awful racket. Most of the jocks do production with -20 as a supposed limit so they won't get into the noise. This has to be a common thing on the Sony Minidisc, because this station has two and they are identical in this aspect.

RiRo

farss wrote on 1/9/2004, 1:21 PM

No, the difference between peak and RMS relates more to having peak and average metering. The average display is trying to give you an idea of how loud it will sound, the peak metering is to stop you clipping.

The integration period of the loudness indication would be in the order of 10,000 samples. The peak indication is probably around 5 samples. The point is that within those 5 samples say 4 of them are 5 and one is 9. The average is 5.8. So we might say we'll display 5.8 as indicating a 0dBFS peak. But if all 5 values in the sample period are 9 then the average is 9, that has to display greater 0dBFS.

Hope that makes sense.

jorgensen wrote on 1/15/2004, 5:15 AM

Vegas uses 32-bit floating-point internally and all (to my knowledge) plug-ins support this directly.

Therefore the only way you can overload Vegas is when the 32-bit FP signal is converted to a 16 or 24-bit fixed point format. This means you do not have to worry about peaks, as long as you remember to lower the level at the final stage, which should be a compressor/limiter with noise shaping.

One can then argue, that the meters should not have a max level of 0dB, but instead +6dB, or preferable, user specific.
The SF7 has tried to add new meter, but they are somewhat strange about the 0dB level.

Rednroll wrote on 1/15/2004, 9:57 AM

Jorgensen,
Where did you get this information from? It is blantantly just wrong. The metering in Sound Forge is only strange to people who don't understand the differences between a peak meter and a VU meter.