[LAU] Gain and clipping wav -> lame

[Martin Cracauer]

Fons Adriaensen wrote on Thu, Jul 25, 2013 at 07:40:53PM +0000: 
> On Thu, Jul 25, 2013 at 02:21:50PM -0400, Martin Cracauer wrote:
> 
> > Does anybody know why wav files that do not have clipping would clip
> > when encoding them with lame?
> 
> Because the peak sample value says nothing about the real 
> level. Take a square wave with peak values +/-1. It is the
> sum of a number of sine waves, with frequencies  1,3,5,7,...
> times the frequency of the square wave. The first one has
> a peak value of about +/-1.27, that is +2 dB. So any encoding
> that looks at the spectrum (and mp3 does) will see a level
> that is +2 dB.

Ah.  Makes sense.  Thanks so much!

Is there a rule of thumb how many db less I should give music to avoid
this? What would be the value for pink noise starting at 40 Hz?

> If you really want to normalise on the peak level, use a 
> lower one. If you want all your samples to have the same
> loudness, use RMS instead of peak, or a real loudness
> measurement such as provided by ebumeter.

Is there a way to hook up ebumeter to just an audio file or a stream
not associated with real time? It seems to come in a jack package only.

Thanks again
Martin
-- 
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Martin Cracauer <cracauer at cons.org>   http://www.cons.org/cracauer/