Quote:
Originally Posted by dcollins  All true and well-put! We generally see an integration time of more like 300ms for things like VU meters, though, but it's a minor point.
The problem with viewing an audio signal as the total energy, is that full-scale 20Hz and full-scale 20kHz sines measure exactly the same. And you probably can't hear either one!
Without some kind of weighting, RMS has little connection to the apparent level of music.
DC |
Absolutely!! By work I meant in the classical 'thermal' sense. As Dave points out two signals with the same RMS value can be very different in percieved volume and tone... although in narrow ranges, and in calibrated situations, the RMS level can be an indicator of 'loudness' (Controlled Situlations).
This is taken advantage of in RMS level gain control and compression. In these applications, it is common to see varying time constants that can get shorter than the 'balistic standards' used for VU meters (published in various specifications for VU meters and indicators).
Some DAW meters allow the RMS time constant to be set. The longer the averaging time, the slower the response, but the more accurate for longer term signals.
When looking at the properties of an audio file in total, such as the statistics window in Audition, the RMS value is reported, the averaging interval being the entire song length. Some posts that I have seen, use this statistics number to report the approximate 'volume' or loudness of a song, which is misleading for a whole song.
Making a relative comparison of the full song RMS pre and post compression and limiting, gives some idea of the loudness increase, but is somewhat academic for a whole song, but valuable for sections of songs with the same program material loudness.
One thing to clear up, the RMS voltage or current is NOT a measure of enrgy by itself. The actual thermal energy created, is a function of ((V(RMS)**2)/Resistance)*Time, which is the integral of the power, or power times time.
If our voltmeter says that a voltage source is 110V RMS, we may not be able to source a 110 AMPS RMS, connected to a one ohm resistor, so here, the fact that we have a 110V RMS, the indication of available potential energy is not valid for this particular source load combination.