Question: Is it possible for an audio recording to have an RMS level in excess of 0 dBFS?
Bonus rep points to the first one posting the explanation as to how this can be!
No takers, eh? Probably should be posted in Mixing/Mastering...
Another way to ask the key question is, why do sine waves show up with the same peak level and RMS level on proper digital audio meters, when mathematically that isn't true?
The answer is that the standards demand it! Sine waves show up with the same value for peak and RMS because the reference value is chosen the same for both measurements to accomplish this.
Even though it isn't mathematically true, this is a good thing, because it gives consistent results and allows you to calibrate your system using a sine wave (or an RMS-calibrated noise file). Put another way, in a band-limited system using a square wave to define levels is a bad idea.
The following is an extract from the International Standard for digital
audio measurements, IEC61606:1997
"3.3.2 Signal level
All digital signal levels in this standard are given in dBFS, defined as
the value of the result obtained from the following equation.
Signal level (dBFS) = 20 log (A/B)
where:
A is the amplitude of the signal whose level is to be determined.
B is the amplitude of a sine wave that corresponds to full scale.
NOTE - Both A and B should use the same method for characterizing
levels,"
Note that both RMS and peak values are referenced to a SINE wave that just reaches full scale up and down.
So, if you use dBFS with RMS measurements then the maximum level you can have is +3.01 dBFS. This level can be achieved with a square wave (or pulse wave) which has only full negative and full positive values. This is because a square wave peaking to full scale has twice the power, or root 2 times the RMS value, of a sine wave peaking to the same value (which happens to be defined as 0 dBFS for both RMS and peak measurements).
Now you know that the absurd is true! So, I'm wondering: has any pop recording achieved an RMS value greater than 0 dBFS? If not, when will we reach that glorious day?
Cheers,
Otto