Re: [LAD] Calculate R M S

Hallo!

> I wanna normalize my sound stream by loudness (energy / pressure /
> intensity) , not by peaks.
> How i do it ?
> Is available Jack plugin for so what ?

You might look into the replay gain standard:
http://replaygain.hydrogenaudio.org/

There is also a libreplaygain somewhere around - look also at
http://en.wikipedia.org/wiki/Replay_Gain for implementations.
(I have also seen once a small commandline program for replay gain
normalization, can't find it ATM ...)

> What is (we hear as) "loudness" ?
> RMS or +(average) or something else ?

That's not as easy as one might think ...
Calculating the RMS level is a good start, but there are other things to
consider:

- from the replay gain side: "The human ear does not perceive sounds of
all frequencies as having equal loudness. For example, a full scale sine
wave at 1kHz sounds much louder than a full scale sine wave at 10kHz,
even though the two have identical energy. To account for this, the
signal is filtered by an inverted approximation to the equal loudness
curves (sometimes referred to as Fletcher-Munson curves)."

- Try e.g. to calculate the loudness of speech: the RMS value will be
much lower as perceived, because during speech there are periods of
silence which are included in the RMS calculation, but we perceive the
loudness only from the parts where the voice is active.
Replay gain tries to consider this problem by doing some statistical
post-processing (see
http://replaygain.hydrogenaudio.org/statistical_process.html).
However, there are different approaches for that: e.g. only calculate
the RMS value from regions where the voice is active (requires some
voice activity detection).

LG
Georg

-- 
http://grh.mur.at
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