Re: RE: RMS meter display calibration
2016/06/21 21:59:14
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I'm not trying to be difficult, but I've been through AES17 a few times over the last several years, and I went through it again tonight, and I don't see anywhere that it states that "a 997 Hz full-scale sine wave should read 0 dB RMS". To be honest, I'm not really sure what that means?
Any dB measurement requires a reference - we have dBu, dBV, dBm (heaven help us), dBFS, and so on.
The other fly in the ointment is that dB is, by definition, an RMS measurement, and it is not well suited to peak measurements.
The other fly in the ointment (who left the door open) is crest factor - the ratio of peak to RMS value of a periodic (or non-periodic) waveform. A sine wave has a peak instantaneous level that is 3 dB greater than the RMS value.
A 997 Hz sinewave that peaks at full scale in the positive direction, and does not reach full scale in the negative direction is considered 0 dBFS, or "all ones" or whatever you wish to call it. It has nothing to do with analog levels, and has very little to do with digital metering, except that in theory that is the maximum measurable level (ignoring all the inter-sample stuff of course.)
I've fed test signals into Sonar from calibrated test equipment and the meters have behaved - they are NOT VU meters, but they do provide reasonably accurate RMS and Peak readings. It's been a while since I've tested the metering, and I too would love to be able to set a threshold, e.g. 0 dB on the meters is some specific (arbitrary would be nice) dBFS value. That would be handy for folks using K-Metering, and in fact handy for the rest of us too.
I seldom pine for the days of analog any more - aligning 16 meters on one tape deck two on the others, and 48 meters on the console was NOT fun, but... if you were patient you could get all the meters to read 0 VU at the same level. And you could even choose your reference level (with in reason).
Nah, I'll stick with digital, and just hang a decent set of analog VU meters off the 2-Mix!
-- Bill
Audio Enterprise
KB3KJF