On Wed, Sep 26, 2012 at 12:08:00PM +0100, Chris Cannam wrote: > On 11 June 2012 18:47, Robin Gareus <[email protected]> wrote: > > Anyway, some of you who package or copied code from meterbridge may be > > interested in this as well. > > [...] > > // def = (db + 60.0f) * 0.5f + 5.0f; // 5.0 .. 10.0 // bug? v0.9.2 > > def = (db + 60.0f) * 0.5f + 2.5f; // 2.5 .. 7.5 // fix! > > You're quite right -- I just double-checked the standard and your fix > is the right one. I have cargo-culted this code into a couple of other > places myself without ever seeing this mistake, so I'll have to fix > those.
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, -- 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
