The electrical way of thinking may be useful too; RMS value is the DC equivalent value to an AC stream.
The RMS value of an alternating voltage or current is the same as the level of direct voltage or current that would be needed to produce the same effect in an equal load.
As the RMS value is mostly used in audio, it's not a bona fide DC. The value changes with time unless all of the audio is analyzed at once. A fairly slow response with lots of input samples(or time, in analogue) is needed to get a decent "steady state" value from the musics alternating waveforms. VU meters are 300 millisec. I usually prefer faster. Somewhere around there is not too far off the response in the hearing.
Andreas Nordenstam
PS: peak level is not only different from RMS, it's different from peak level too! there's sample point peak level and there's the peak level of the signal in between the sample dots. this link can't be repeated too much, hope it's al right:
http://www.cadenzarecording.com/pape...distortion.pdf