[Ben Bradley[_2_]]

On Fri, 19 Nov 2010 16:33:53 -0500, Randy Yates
wrote:

Hi,

Some had responded here to my recent inquiry on levels that dBFS is a
peak measurement.

If an RMS measurement needs to be made for a digital signal (i.e., on a
digital mixing console or a ProTools plugin), what units are utilized? I
thought they were dBFS, i.e., that dBFS was an RMS measurement.
Apparently I am incorrect. Somebody please set me straight.

What an interesting thread. It's funny the things that get argued
again and again ... good to see that Usenet is still alive!

My answer is that dBFS is a peak measurement (and most likely of
samples, not of a reconstructed waveform, which could be higher) as
displayed by the bargraph "meters" in most recording software, unless
it says it's something else. The something else is usually RMS.

There's been debate in this thread about bits vs. voltages (or
power, which is the "root" (sorry) of the RMS voltage measurement). I
really see no conflict here. The dB levels calculated with bits (more
specifically, linear PCM representations of discrete sampled voltages)
are the same as when the samples are put out through DAC's and the
relative voltages measured and the dB values calculated from those.
The numeric values are just binary representations of voltages, and
the values are calculated the same way. The dB value is the ratio of
two values of power, or two values of RMS voltage into a fixed
resistor, or between two sets of samples whose RMS values are
calculated.

This reminds me of a thread I read here (rec.audio.pro) long ago on
dBFS RMS measurement, and how one recording program did it.

First is a setup thread, "The Crest of the Wave (reference stuff!):"

http://groups.google.com/group/rec.a...213daf805e93c9

Next, the thread I remember: "RMS in CEP, just in from Syntrillium"
(that's Cool Edit Pro, presumably used the same RMS code as Cool Edit
96, both by Syntrillium before Adobe bought it all and renamed it
Audition):

http://groups.google.com/group/alt.a...cacf7552df88d7

I hope that sheds more light than heat. It's also notable that
there are several participants in those 11-year-old threads that are
also posting in this one.