On Wed, Sep 26, 2012 at 01:23:48PM -0400, Gene Heskett wrote: > On Wednesday 26 September 2012 12:58:35 Fons Adriaensen did opine: > > > There is more to fix. > > > > The meterbridge website still claims that those meters 'almost' conform > > to some standards while in fact they even don't come close. > > > > According to the standard, a VU measures the average of the absolute > > value. For a steady input signal around 1 kHz, it must rise to 99% of > > the real value in 300ms and overshoot it by 1 to 1.5% before falling > > back to 100%. The one from meterbridge measures RMS and rises to the > > final value in around 5.3ms, that is more than 50 times too fast (at > > a sample rate of 48 kHz, and worse for higher sample rates). > > > > According to the standards, a PPM or IEC meter must have a controlled > > rise time of 5 or 10ms (depending on the standard). The one from > > meterbridge indicates peak sample values instead. > > > > Ciao, > > You are very correct, Fons. However, as a BC engineer, I have observed > severe clipping of the waveforms because they exceeded the headroom of the > DA's, which in this case was _+28 dbm, while the true vu meter sitting on > that same line was reading -3dbm peaks. For average loudness readings the > legal and pricey vu meter is fairly accurate, but it fails to detect the > transients in todays music, or even in tv's spoken dialog during a soap, > where the human ear as assaulted by the clipping cracklies the 70 year old > analog std meter simply doesn't detect. To that end, the best production > audio boards are also equipt with the much faster LED setups that latch > such a peak condition excursion for at least 100 milliseconds to make it > obvious a peak has been exceeded. > > To that end, the operators under my control have always been instructed to > take it down a snudge until the overload LED at +16dbm only blinks at 5 > second or more intervals. Listener fatigue can be very apparent in much of > todays audio streams when the old 'vu' meter is peaking at _+4. > > And it shows in the ratings books when those instructions are being > ignored, folks might be fans of the program but something they only 'feel' > makes them channel hop looking for a more pleasant experience. When 1 > point in the ratings is as important as it is to a facilities cash flow, we > look for every conceivable advantage. Bad audio hurts.
All very true. But that's no reason to claim that something that just looks a bit like a VU meter but behaves *very* differently actually is a VU meter. Same for the PPMs. The code to this correctly has been available and GPL licensed for 4 or 5 years now (jmeters), so there's no excuse. Ciao, -- FA A world of exhaustive, reliable metadata would be an utopia. It's also a pipe-dream, founded on self-delusion, nerd hubris and hysterically inflated market opportunities. (Cory Doctorow) _______________________________________________ Linux-audio-dev mailing list [email protected] http://lists.linuxaudio.org/listinfo/linux-audio-dev
