On Sat, 24 Oct 2009 12:51:59 +0200
fons@email-addr-hidden 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@email-addr-hidden http://lists.linuxaudio.org/mailman/listinfo/linux-audio-userReceived on Sat Oct 24 16:15:01 2009
This archive was generated by hypermail 2.1.8 : Sat Oct 24 2009 - 16:15:01 EEST