[LAU] Focusrite Scarlett 18i8

[Robin Gareus]

On 01/08/2014 02:41 PM, Fons Adriaensen wrote:
> On Wed, Jan 08, 2014 at 05:05:48AM +0100, Robin Gareus wrote:
>  
>> I can't confirm neither directly. But I think it works these days:
>>
>> http://focusritedevelopmentteam.wordpress.com/2012/04/23/linux-and-focusrite-novation-products/#comment-104
> 
> Interesting.
>  
>> The reason I lost interest is that I think the device is crap.
>>
>> The volume dials don't latch. I set a gain on the Focusrite 18i6 and a
>> minute later it's off by +-1dB.
> 
> The 'rubber controls' effect.
>  
>> Compared to the other two USB audio-device that I have, the [preamps of
>> the] Focursite 18i6 is the noisiest.  Measured with a 200 Ohm
>> termination and jnoisemeter: ~-72dBFS (Flat, RMS) -- the Edirol UA-25 is
>> at -81dBFS and the Presonus 1818VSL at -84dBFS.
> 
> Those numbers by themselves mean nothing, you need to consider the gain
> as well. If e.g. the 18i6 has 9 dB more gain than the UA-25 then they
> have the same input noise.

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.

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.

I also have one of them each. So maybe I was unlucky to get a bad/good
device. I also did not have access to pro-equiment to calibrate &
measure them, but identical equipment was used to evaluate all.

>> That make we wonder which award those 'award winning' preamps of
>> Focusrite actually won :)
> 
> A marketing award ?
>  
>> It has gain labels from 0..10 -= other comparably priced devices have
>> latched dials properly labeled and calibrated with dB.
> 
> If you can trust those dB marks is another matter...

right. They don't need to be exact to the degree but at least give an
indication. "About +5dB" is more useful that just a number, IMHO.

> I'm enquiring about this for a friend who needs an USB card to be
> used with the RPi, with 4 mic inputs. Application is environmental
> noise monitoring AFAIK. All suggestions welcome !

The form-factor of the 18i8 is probably a bonus in this case.

Skimming over http://wiki.linuxaudio.org/wiki/hardware_support
the only comparable device would be the Alesis iO4 (unless you also
consider more expensive equipment with more than 4 inputs).

for environmental noise measurement, the devices do not need to be
sample-sync, do they? You could probably use two stereo USB1 devices.

best,
robin