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From: sandell@batcomputer.tn.cornell.edu (Gregory Sandell)
Newsgroups: comp.music,sci.psychology
Subject: Re: Quantifying Digital Sound Loudness
Keywords: psychoacoustic sound algorithm loudness
Message-ID: <1991Feb14.170438.21847@batcomputer.tn.cornell.edu>
Date: 14 Feb 91 17:04:38 GMT
References: <2112@fornax.UUCP>
Organization: Cornell Theory Center
Lines: 40

In article <2112@fornax.UUCP> laughlin@fornax.UUCP (Bob Laughlin) writes:
>
>    Hello,
>
>   I am looking for information on algorithms that can be applied
>to digitized sound data that yield psychacoustically relevant
>measures of "average sound level" and "dynamic range". 
>These measures would be computed at specified intervals
>over the duration of the sound (say at 200 ms intervals).
>"Average sound level" should yield a measure of the overall
>sound intensity over a given interval and "dynamic range" 
>should yield some measure of contrast between loud and
>soft sounds over some duration.  If anybody knows of relevant
>literature on this I'd appreciate it if you emailed it to me
>or posted it here.  Thank you.
>-- 

DIGITAL SIGNAL PROCESSING OF SPEECH SIGNALS by Rabiner and Schafer
provide some good material on calculating sound level from 
samples.

A real simple measure is RMS energy.  Over the duration interval
you want to measure, square each sample (to get rid of the sign)
and keep a running sum.  Take the mean of that sum, and take its
square root.

You might want to convert this measure to dB power.  Assuming we
are talking about 16-bit samples, you could try using this:

10.0 * log10(amp/32767.0)

This will represent the most intense signal as 0 dB and all other
levels as negative.

I can give you some references to classic literature on loudness
calculation.  However, much of that will be included in the
bibliographies of Rabiner & Schafer.  Let me know if you need
more.

Greg Sandell