On Wed, Sep 26, 2012 at 12:08:00PM +0100, Chris Cannam wrote:
> On 11 June 2012 18:47, Robin Gareus <robin@email-addr-hidden> 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 Linux-audio-dev@email-addr-hidden http://lists.linuxaudio.org/listinfo/linux-audio-devReceived on Wed Sep 26 20:15:02 2012
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