Re: [LAU] Focusrite Scarlett 18i8

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)
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