Can 2 focusrite Scarlett 18i20's (USB) work with SONAR X2 to get 16 XLR MIC ins?

 
My first forum post ever...
I'm a newbie building a studio with SONAR X2, wondering if I can get it to work with 2 focusrite 18i20's to get 16 XLR MIC inputs.  I am aware that tying a Octopre MK II to the Scarlett 18i20 will give 8 more XLR ins through ADAT, but only 4 at full 96KHz recording.  I hear there are issues with DAWs seeing two of the same units via USB and combining inputs.  Thoughts?

ASIO driver mode only allows a single driver/device instance (unless the ASIO drivers are specifically written to support "device aggregation", which afaik Focusrite's aren't), although WDM mode may allow using multiple interfaces. But I don't even know if MixControl can work with more than a single interface connected by USB. In any event, the interfaces would need to be synced together digitally.
 
The 18i20 can operate in "stand-alone mode" after being set up using MixControl, so it should be possible to set up a first 18i20 in stand-alone mode having its inputs routed to its ADAT output and connected to the ADAT input of the second 18i20 (what is sometimes referred to as "converter mode"). Haven't actually tried it though, so dunno.
 
But imo it would make more sense just to use an 8-input preamp/converter with ADAT output like an Octopre or Digimax, etc. for adding more mic inputs, and/or use a different interface offering 2x ADAT S/MUX inputs if you really need 8 more inputs at 96kHz.

You definitely want to take a look at your ADAT options. If you can get by with average preamps, or if 8 or more of your inputs are line level, the Behringer ADA-8000 is a low cost option to bring an additional 8 channels into the digital recording bitstream, and you'll probably find uses for the extra 8 outputs as well. Prices go up from there.
 
If you already have the second Focusrite interface, all you need is an ADAT cable, aka Toslink. Controlling the second interface then becomes the next issue to solve. The Behringer requires no external control software. Each input has its own pot for gain control, there's a button to turn Phantom Power on/off, another switch to set sync to internal or external, a power button and that's pretty much it. Very simple. If you go that route, you want to think about your physical input and output connectors. You have a choice of balanced XLRs or quarter inch for the inputs, outs are XLR only, and you can run into some expense there.
 
I use an M-Audio 2626 Firewire interface as my primary, with the control software on the Sonar PC. I have a pair of the Behringer 8000's into the 2626's two ADAT ports for a straight 24x24 I/O setup, however, I hung an M-Audio Fast Track Ultra off of a second PC, and it feeds the 2626 via stereo SPDIF, giving me an extra 8 ins and outs but only two channels at a time. From one point of view it brings the system up to 32 ins and 32 outs, but with a 2x2 bottleneck between the 24x24 I/O Profire and the 8x8 Fast Track Ultra, so I generally work with the assumption of 26 ins and 26 outs. There's are a couple additional complexities regarding the Fast Track's I/O but 26x26 operation is straightforward and simple, so I won't go into those.
 
I've been known to push the gain and SPLs real hard during playback and practice, and I'm not getting ANY noise from the 2626, the Behrs, or the Fast Track. I do get some additional noise floor from my outboard loops, the pair of Lexicon MX200s are most noticable, with lower additional noisefloor from 8 DBX comp/EQ loops when I run them hard, but...
 
I record dry with respect to ambience, the Lexis are for the headphone/monitor setup unless I have reason to patch them differently, so the noise doesn't make it into recordings. I sometimes adjust dynamics and or EQ on the way in if I think I'll really need it later on, one bass player in particular has a...let us say, very dynamic approach, and some vocalists track better after being stepped on a little. In noise problem cases, I can bypass the comp/EQ loop if need be, and/or repatch so the dynamics and EQ only affect the phones/monitors like the MX200s. Guitars and bass are a bit noisy to start with, so the EQ/Comp loops noise is well down in that soup, inaudible, and even the Lexi noise isn't noticable on driven bass or guitar except between notes.
 
Point of this being...NONE of the noise issues are fatal, none HAVE to make it to tape, and NONE of them stem from the 26x26 ADAT and SPDIF multiplex, even pushed hard.
 
There IS one issue you'll run into sooner or later expanding like this. There is a practical limit how many hi res audio channels a given PC can record at once. I believe that limit to be right around 26 input streams at 16/44, but haven't tested it personally. From what I've heard, you're coming up against both Firewire and PCI buss limitations there, on the mathematical, design spec side.
 
In actual practice, your computer hardware and OS optimization may impose additional limitations. I don't think you'd have to work TOO hard to get 16x16 I/O at 16/44, with any competent i5 or i7 processer, less sure at 24/44 or higher.
 
That said....if you do run into buss or processor limitations, it MAY still be possible to lay down a full 16, 24, or even 26 simultaneaus tracks, IF you and the boys are all monitoring thru the zero latency DSP processor in your primary interface. You might have some SEVERE lag and latency in what's going onto tape, BUT...you won't hear that during tracking, and you MIGHT not notice it at playback because even though there was delay between what you heard at tracking and what was going onto tape, it MAY have all been subject to similar lag and still be in sync.
 
If you DO have problems, I'd imagine they will either be some tracks out of sync with others, and, a little further down the "you're pushing it bub, now ya pay" trail, you'll get pops and crackles as too much data is flowing thru too skinny pipes, some is lost, standard term is dropouts.
 
One more hint. The zero latency DSP processor and software in many interfaces doesn't HAVE as many channels as you can run thru it if you plug all your holes. I may be able to record 26 simultaneaus tracks, but I can only monitor 18 at a time. Pushing things like this rules out say, a drums submix or buss from the DAW software mixed with the live DSP monitor channels because of the lag mentiuoned above. But no law says you have to monitor in stereo, EVEN if you are recording in stereo. I've had a lot of musicians wanting "more me", but so far, nobody needing panned a certain way on the cans. If somebody ever does need a certain placement in the stereo field, that's something they already told me before we set up, because I asked, and if they've changed their minds since, they're paying hourly. At that point, the 8x2 nature of the Fast Track Ultra's connection to the main  interface gives me some stereo options that aren't too DSP channel hungry.

Matt.Focusrite
Only one 18i20 can be addressed by Sonar at a time, but as Goddard mentioned, the second 18i20 can be set to operate as a standalone preamp with A/D and D/A conversion like an Octopre.  To do this, you will need to connect the second 18i20 to the computer by itself and then in the routing section of Scarlett MixControl, set the source for the ADAT outputs to analog inputs in a 1:1 fashion (ie. Anlg In 1 -> ADAT output 1, Anlg 2 -> ADAT output 2, etc.).  Make sure that the sync source is internal and the sample rate matches your desired sample rate.  Now go to the File menu and select 'Save to Hardware'.  Now disconnect the 18i20 from the computer and connect the other one.  For the 18i20 that will remain connected to the computer, set the sync source to ADAT.  Connect an optical cable from the ADAT output of the standalone 18i20 to the ADAT input of the 18i20 connected to the computer.

Hi Matt, and thanks for your input. Nice to see participation from Focusrite here.
 
Just out of curiosity, which other Focusrite interface models can operate stand-alone and as a preamp/converter?

Thanks for that info, Matt! Good to know.

I think they all do that. Although not the same manufacturer mine does that. Faster sample rates  = less channels.
 

I went  the cheap route to get more inputs for my 18i20, I got a cheap ADA8200 for $200.  That gave me 16 channels of recording in X3 (and it sounds fine for the price for the rock and metal I usually record).