8 Jan
2014
8 Jan
'14
4:43 p.m.
On Wed, Jan 08, 2014 at 03:51:41PM +0100, Robin Gareus wrote:
I had calibrated -18dBFS on all of them to the same
source (a 1KHz sine,
which I believe to be 0 dBu). That's how I found out about the rubber
controls effect in the first place.
O dBu ? So you measured the line inputs, not the mics ?
On a real pro device the line input would bypass the mic
preamp. OTOH, on most cheap cards it's just attenuated and
fed into the preamp - the perfect recipe for bad S/N.
I also did two another measurements, setting the
gain-dial of each
devices at minimum and maximum. The 18i6 still came out worst.. but that
is not too unexpected. The gain range of the 18i6 is about -10dB ..
+30dB (per specs it should be -10..+36), while on the other two it's
-20dB .. +20dB.
'Gain' for an A/D converter is not really defined - the ratio of a
purely numerical value (in the digital domain) and a physical one
(the actual input voltage) is has a physical dimension (1/Volt).
So that is not a 'gain' in the usual sense.
For a 'gain' spec to have any meaning at all
* it should be the analog gain from the input connector
to the analog inputs of the converter chip (but don't
assume that is what the specs mean),
AND
* you need to know the actual full scale voltage of the
converter chip.
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)