Re: [LAD] [ANN] Invada Studio LV2 Plugins 1.2.0

On Sun, Aug 23, 2009 at 05:44:55PM +0100, Dan Mills wrote:

> The VU is a slow response meter (300ms integration time IIRC)intended to
> (badly) track perceived volume,

The VU specs are based on what was possible 50 or
more years ago. A typical VU would just be a diode
bridge and a series resistor feeding a moving coil
meter, and no active electronics (you had to drive
them using a separate line amplifier to avoid
distortion caused by the diode bridge).
That means it measures the average of the absolute
value (and not RMS), and the dynamics are defined
by a second order filter acting on the rectified
value. For a sine signal corresponding to 0 VU the
meter should reach 99% in 300ms, and overshoot by
between 1 and 1.5% before returning to the correct
value.

> The differences each time you play are why we leave the thick end of
> 20db of headroom between 0 VU and 0dbFS, you should (in a production
> environment) never be going anywhere near 0dbFS (there is no need for it
> in the age of 20+ bit ADC noise floors).

VUs are not very useful today. On one side, the
digital domain does not overload as gracefully
as magnetic tape, so you should be conservative
and use e.g. -20dB digital = 0 VU.
On the other hand some of today's commercial music
is so heavily compressed that a VU calibrated like
that and used on a final mix would go off scale well
before there is any digital overload. In that case
you'd want a different calibration, even less than
the historical one which was around 9 dB below 'peak',
with peak being a somewhat softer limit than it is
today.

So if you still want to use a real VU it almost has
to have variable calibration, which is a bad idea
as it doesn't allow you to form any stable mental
picture of the relation between loudness and the
meter indication.

Combining a true RMS and a digital peak meter in
one display without any gain difference between
the two is IMHO the best way to go, and it is
exactly what e.g. the K-meter does.

Ciao,

-- 
FA
Io lo dico sempre: l'Italia è troppo stretta e lunga.
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