23 Aug
2009
23 Aug
'09
7:07 p.m.
On Sun, Aug 23, 2009 at 07:27:18PM +0100, Dan Mills wrote:
Lets say your card is aligned so that 0dbFS = +18dbu
(EBU standard),
then 0Vu = +4dbu = - 14dbFS, so a software VU calibrated for 0Vu =
-14dbFs should read the same as an external Vu calibrated for +4dbu =
0Vu. If it does not then either a calibration setting is off somewhere
or one of the meters is faulty.
True.
But even a definition such as 'dB FS' is ambiguous, and
it's easy to make mistakes as a result of that.
Consider a sine wave that is just below digital clipping.
This would be called '0 dB FS', but the actual RMS level
is 3 db lower. I've seen at least one context where this
same signal would be called -3dB FS. Which somehow makes
sense as well.
AFAIK the first interpretation is the more common one.
actually fairly common with professional cards.
And it avoids a lot of problems. Semi-pro cards will not
have the correct levels, but some can be quite consistent
between channels. For example my Terratec EWS88MT has less
than +/- 0.1 dB variation between its 8 channels, both
for input and output. But the actual level is just +3.5dBu
for a FS sine wave.
The real misery starts when (as reported in a recent post
on LAU or LAD), a user finds four volume controls between
his audio file and the physical output (plus of course
a fifth one on his amplifier), and then of course gets
confused on how to set all of them.
Ciao,
--
FA
Io lo dico sempre: l'Italia รจ troppo stretta e lunga.