Re: [SoX-users] To normalize volume level in a file

[Joel S. <joe...@ho...>]

Does --replaygain prevent clipping?  Or does it simply apply a gain based on
the RMS peak volume level (which will be less than the actual peak sample).

On 8 September 2011 09:47, Fmiser <fm...@gm...> wrote:

> > Safiye Turgut (Garanti Teknoloji) wrote:
>
> > Two methods are appropriate for us. But we choose the second
> > method that you said turn up the quiet portions but leave the
> > loud parts the same.  All of parts level should be same.
> >
> > How can I do it?
>
> With the compand effect.  The man page and "soxexam" have
> information.
>
> The "compand" effect can be setup as a compressor, or expander,
> or AGC.
>
> Technically, an AGC is a compressor with a make-up gain with
> the controls "turned around" so the target level is set rather
> than trigger point.  The compand effect can do the same thing.
>
> I usually use the "play" command to fiddle with the values.
>
> Command [infile] [effect] [attack time],[release time]
> [knee] [in dB],[out dB] [gain] [initial level] [delay]
>
> To make more even slow changes try:
>
> play file.wav compand 1,4 6:-80,-80,-75,-25,0,0 -5 -30 1
> This will make a very slow change - maybe too slow. And it
> won't help at all for short, quick sounds - like if someone
> bumps the mic.
>
> So, to clamp down on the short duration noises
> play file.wav compand .03,.2 -80,-80,-15,-15,0,-15 -15 -40 .1
>
>
> Those strings of numbers look daunting, but don't let them
> scare you.
>
> The first two are attack and release - like any compressor
> would have. The smaller the number, the "faster" the response
> time. So to have the gain adjustment not be affected by a
> single hand clap, or a book dropping set the attack
> slower. Release is then how quickly the gain adjustment "lets
> go" of the signal.
>
> The next set of comma separated numbers are a map. Meaning "if
> the input level is -80, make the output level -80". The next
> pair is "-75,-25". This is a 3:1 ratio compression. And until
> there is another number pair, it will treat all the levels
> in between with the same ratio. Below is another way to see
> it, the numbers in parentheses are implied.
>
>    0      0
>  (-3     -1)
>  (-6     -2)
>  (-12     -4)
>  (-18     -6)
>  (-30    -10)
>  (-45    -15)
>  (-60    -20)
>  -75    -25
>  -80    -80
>  IN     OUT
>
> After the pairs is an overall gain.
>
> That is followed by a "starting position" gain level. Since
> the whole point if the effect is to respond to the input
> signal over time, it takes time to adjust at the very start of
> the file. This lets _you_ guess what the incoming audio level
> will be to give the effect a head start.
>
> The last number is how far behind the measuring should the
> adjusting occur. Nearly always having it match the "attack"
> value is best.
>
> With the first command, the compand part is adding gain. In
> the second command I turn that around. I set the attack and
> release much faster. then instead of turning up the output as
> compared to the input, I turn down the output.
>
> After processing the audio with both of these, I would apply
> some form of "normalizing". Sox can only do this with peak
> values - which do _not_ correspond to how our ears will hear
> it.  There is a linux tool called "normalize-audio" that bases
> it's gain adjustment on RMS values, not peak, which makes it
> a much better match to what we hear.
>
> Better yet would be what's called "replay-gain".  This uses RMS,
> statistical analysis, and EQ filters to make it an even better
> match to how human ears would hear it.
>
> I have used the linux tool wavegain as well as vorbisgain and
> metaflac.  I think wavegain is the only one that will actually
> change the file.  The other ones just create a tag so the
> playback software can adjust the level accordingly.
>
> -- Philip
>
>
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