Measuring Dynamic Range 2008-06-16 15:53:22 Having read some of the many discussions about ReplayGain and the Loudness War, I had some thoughts about how to measure, not loudness, but the dynamic range actually used. Most people are just eyeballing the waveforms in their favourite sound editor, but I'm sure we can do better than that.My main thoughts take advantage of the fact that there are two kinds of level meter typically used in production and broadcasting - VU meters, which specifically measure "average" level over a short period, and Peak meters, which do what they say on the tin. The BBC, for example, much prefers to use a PPM (Peak Programme Meter) than a VU.A VU meter has slow ballistics, which is to say that it takes about 300ms to get within spitting distance of the sound it's measuring. Therefore, it tends to miss most transient sounds, but it responds well to syllables of speech.A PPM meter has fast, but not instantaneous attack ballistics - it will not respond to (perceptually inaudible) clicks, but it will respond fully to a drum hit. Since it uses a "lossy quasi-peak detector", it then decays quite slowly from the peak it has measured. I believe the attack time for a BBC-spec PPM is 20ms to 90%, but I could be wrong - and different European broadcasters use different, but broadly similar, attack specs. The decay time is measured in seconds, giving the engineer plenty of time to note the peak level.As a result, for a steady tone both meters will read the same, but for speech and music the PPM should normally read higher than the VU. This is reasonably well-known, at least by people who know that different kinds of level meters even exist.How *much* higher is a function of the local dynamics of the measured sound - and this is the principle I want to use.I think that the differential between a VU-like meter and a PPM-like meter could be a valid and useful measure of dynamic range, just as ReplayGain is a useful measure of the "progress" of the Loudness War. It should allow people to quickly determine whether the mastering of a particular recording is likely to be any good, regardless of level. It would probably be better if the decay rates of the two meters were more similar.Now before I dust off my Model M and start coding, are there any comments from the locals?