Re: Creating files with RMS gain level instead of Peak

[James Trammell <james.trammell@gmail.com>]

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Måns,

Perhaps the following information will explain what I am seeing.

Files

1.
http://substrate.com/rms/sox,noise,white,stereo,24b,96000Hz,m12dBFSpeak,tpdf,10s.wav

Stereo white noise created by SoX; a 24bit 96kHz file at -12dBFS Peak and
10s duration, dithered with TPDF dither to 24 bits.
SoX invocation: "sox -V -b 24 -r 96000 -n
sox,noise,white,stereo,24b,96000Hz,m12dBFSpeak,tpdf,10s.wav synth 10
whitenoise whitenoise gain -12 dither"


2.
http://substrate.com/rms/rx6,noise,whiteuniform,stereo,24b,96000Hz,m12dBFSrms,tpdf,10s.wav

Stereo white noise created by iZotope RX6; a 24bit 96kHz file at -12dBFS
RMS and 10s duration, dithered with TPDF dither to 24 bits.



Screenshots

3. http://substrate.com/rms/filestats_sox.png

Brief RX6 analysis of the SoX file; notice the peak level is -12dBFS while
the RMS level is -13.76dBFS.


4. http://substrate.com/rms/filestats_rx6.png

Brief RX6 analysis of the RX6 file; notice the peak level is -10.24dBFS
while the RMS level is -12dBFS.


5. http://substrate.com/rms/rx6_whiteuniform.png

An FYI shot of the RX6 dialog box to point out that it only allows
amplitude specifying as RMS; there is no way to enter a peak value.


6. http://substrate.com/rms/rx6_whitechoices.png

An FYI shot to show that RX6 offers 4 flavors of white noise. I chose white
uniform for this exercise because that appears to match what SoX produces.
As a side question, it would be nice if someone here could confirm what
flavor of white noise SoX produces.


To recap what I am trying to do, so that my original question is not lost:
I want SoX, ideally natively via some appropriate command-line switch, to
output a white noise file with a specific RMS amplitude.


Thanks.


On Sun, Jul 8, 2018 at 8:39 AM, Måns Rullgård <mans@mansr.com> wrote:

> Jeremy Nicoll - ml sox users <jn.ml.sxu.88@wingsandbeaks.org.uk> writes:
>
> > On 2018-07-07 21:47, Måns Rullgård wrote:
> >> Jeremy Nicoll - ml sox users <jn.ml.sxu.88@wingsandbeaks.org.uk>
> writes:
> >
> >>> Yes.  So does that mean that the OP should use something like the
> >>> 'stat' effect to find out the peak RMS level of the audio file,
> >>> then work out how much gain or attenuation is needed, then use
> >>> a 'gain' effect with that calculated value?
> >
> >> No, he should just use the gain effect.  It adjusts both RMS and peak
> >> values by the same amount because that is what happens when you multiply
> >> each sample by a fixed amount, which is what the gain effect does.
> >
> > Yes, I understand that gain is gain, but he has to decide how much
> > gain to apply.  If he's previously done that in terms of a pre-gain
> > peak level, but now wants to bring RMS levels to a certain point,
> > he surely has to find out what the file's RMS levels are first
> > then decide how much to modify it by?
>
> The question posed was how to obtain an RMS gain of -12 dB.  The answer
> is that RMS gain is equal to peak gain, so "gain -12" will perform the
> desired function.  If the question were how much gain to apply in order
> to obtain a specific RMS level, then of course the initial value would
> have to be known.
>
> --
> Måns Rullgård
>
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