On Sat, 24 Oct 2009 12:51:59 +0200 fons@xxxxxxxxxxxxxxx wrote: > On Sat, Oct 24, 2009 at 05:51:19PM +1300, Chris Edwards wrote: > > > I used to be put off by meters that looked slow, > > until I realised how useful RMS meters were and > > how long the windowing time needs to be to capture > > the bass frequencies. :) Fons, I've been wondering, > > though, does the update rate in jkmeter affect the > > measurement window, or just the display rate? > > It just determines how smoothly the display will appear. > The dynamic behaviour of jkmeters (and also of the VU and > PPM meters in jmeters) is very strictly defined. The values > that are displayed are calculated in a way that does not > depend on the display update rate, and (within reasonable > limits) also not on the Jack period size. A level meter > would just be useless eye-candy otherwise. > > There is indeed a 'window' for the RMS value, but > don't imagine it as being rectangular, i.e. with > all samples having the same weight. The window is > more like an impulse with a slightly smoothed front > (which determines how it will react to short bursts) > and an exponential decay. It is the impulse response > of a critically damped 2nd order filter acting on the > square of the signal. The controlled fallback of > the RMS indication is not artificial (as it is for > the peak value), it *is* the shape of the window. > > > I've also been wondering what the purpose of the > > fall-of on peak meters is. Why not just reset the > > peak level immediately and let it get bumped up > > again by the signal? > > Even in that case you would need a defined fallback > rate. Lower peak levels should be shown only if they > are not immediately following a much higher peak, > otherwise the peak level will jump up and down all > the time. In other words the bump-up should happen > only if the current input is higher than the fallback > of the previous peak. Having a visible fallback is > easier on the eyes. > > Ciao, Very interesting information. It's fascinating how complicated something like a 'simple' metering system is! -- Will J Godfrey http://www.musically.me.uk Say you have a poem and I have a tune. Exchange them and we can both have a poem, a tune, and a song. _______________________________________________ Linux-audio-user mailing list Linux-audio-user@xxxxxxxxxxxxxxxxxxxx http://lists.linuxaudio.org/mailman/listinfo/linux-audio-user
