chain audio interfaces with ADAT to get more inputs?

[michelrandahl]

I am looking to buy a new audio interface for my small hoby musician project, that currently consists of a handful of hardware synths, an effect pedal, a sampler, a classical guitar and a laptop with Linux and Bitwig. I am basically looking for a way to get as many line inputs (and as little latency) as possible without breaking the bank, and during my research into audio interfaces I came across something called 'ADAT' which sounds promising with regards to chaining audio interfaces together to expand the number of inputs.

I am currently using an old 'Focusrite Scartlett 2i4', which I have been extremely pleased with so far. Its good quality and it hasn't been much hassle to get it working in Linux (after I figured out how to use QJackCtl and installed Linux with the correct settings).
Because of my great experience with Focusrite, I currently have my eyes on the 'Scarlett 18i8' which would give me 8 mono inputs.. However 8 mono inputs is not enough. I downloaded the manual for the 'Scarlett 18i8' and they seem to recommend to pair it with the 'Scarlett Octopre', so it is my understanding that I can buy those two audio interfaces and chain them together with ADAT such that I have 16 inputs available... But, I am still a bit confused and uncertain about this 'ADAT' thing....

Is my basic understanding of ADAT correct? (I mean, can I chain two audio interfaces together to get more inputs?)
Will it be a lot of trouble to get ADAT working with Linux? and will the extra inputs just magically be available in to jack and Bitwig without a lot of effort? (The examples I have found on ADAT configuration, when googling, only shows some configuration done in a program in Windows...)
Will I get a lot of extra latency on those extra 8 inputs? (I prefer latencies around 10ms or less).
What would the latency look like if I paired a 'Clarett 18i8' with a 'Scarlett Octopre' through ADAT? Would the 'Scarlett Octopre' increase the latency for all inputs?
Are there any better options for getting at least 16 line inputs in linux, without breaking the bank and without depleting the space on my already very crowded desk?

[Michael Willis]

Is my basic understanding of ADAT correct?

Yes, the Octopre is designed to be paired up with another device that accepts ADAT input. Be aware that in order to use all eight channels on the Octopre, you will be limited to a sample rate of 48kHz (insert big argument about sample rates and the obligatory link to xiph.org).

It will have slightly more latency. I found an article called Focusrite: OctoPre MkII Dynamic and Saffire PRO 40, which reports that at 44.1kHz the OctoPre adds five additional samples of latency. If I did the math right that's less than a millisecond, so probably not worth worrying about.

You might consider getting the Scarlett 18i20. If you get it used on reverb.com it's not that much more expensive than the 18i8, it has the same rackmount form factor as the Octopre so they would stack nicely in your limited space, and then you would have a total of 16 pre-amps instead of 12.

[michelrandahl]

Thank you very much for the informative links. Sounds like latency isn't something to worry too much about .
Its a good point with the form factor of the 18i20, as they would be easy to stack in the wooden rack that I'm gonna build to fit under my screen (and look nice). However I am unsure if I would ever benefit from those extra preamps since I don't plan to have any microphones (..or maybe just a single microphone) in the setup.
I guess a motivation for getting the 18i20 would be that it has both ADAT in and out, and it even seems to have two of each -opening up for future expansion for getting even more inputs and outputs....
If I understand correctly, the ADAT signals are unidirectional, and thus the extra outputs on the Octopre in a 18i8+Octopre setup, would be useless since 18i8 only has 'ADAT in'?

How is configuration done in Linux wrt. ADAT? Do the devices just sort of configure themselves when you plug them together..?
Or perhaps its just a matter of setting the same sample rate for both devices in QJackCtl (provided that both devices show up in QJackCtl)..?
Or perhaps you need to use Virtualbox with a Windows installation and follow the official configuration procedures in the Focusrite Windows software? (hopefully just once, ever)

[martibs]

I am not familiar with Focusrite devices, so I can't speak to your case. In my case, however, I have ADAT set up using a Steinberg audio device into an Arturia AudioFuse. This required some configuration on both devices, and neither have configuration software available on Linux, so I had to do it on Windows.

Once set up, the AudioFuse device shows up in my system with all the ADAT channels available. I'm restricted to using maximum 48K sample rate. The measured roundtrip latency is quite high, but I guess that comes down to the converters of the older Steinberg device, as ADAT lightpipe itself should not add much.

[NachoRR]

@martibs
Sorry to revive an old thread... I'm thinking on getting an 8pre device, and I can find a used Arturia audiofuse at a good price, but I was reading about compatibility, and some people says it gives probelms (creackings and pops...). Is ti working fine for you? For I can get also a scarlett 18i20, but pres are suposed to be inferior quality. And can also get an Steinberg, but I think it's not working fine in linus (or is it?).

So, I would hear from someone who really owns them.

Thanks!

[martibs]

@NachoRR
I have moved on from the AudioFuse for quite a long time ago. I did not have any issues with its performance. But in the end, the lack of Linux-compatible software made me go for another solution:
I now have a Behringer UMC 1820, with 8 ins and 8 outs, and a Behringer Monitor 1 as a simple volume control on my desk. I'm looking into upgrading to the Focusrite Scarlett 18i20 Gen3, or perhaps wait until they release a Gen4.

[tseaver]

@michelrandahl

Technically speaking, the various "Octopre" devices aren't audio interfaces: they don't do any of the work to present themselves to a computer. Instead, such devices provide multiple mic-preamps (which are also found in almost all audio interfaces), with a facility to send their sound out to another device over either digital or analog connections.

What you want to do is exactly what the Octopre + 18i8 (or 18i20, etc.) are designed for: you get more input channels, without the hassles of persuading your computer to keep two audio interfaces somehow in sync. The sync bit does bring to mind a caution: beyond the ADAT cable you use to hook the separate mic preamp unit (the Octopre, or something like a Behringer ADA8000) to your interface, you will also need a "clock sync" cable: it is likely that you need a separate, coaxial "word clock" cable: one of the devices (almost surely the interface) needs to be the "master" time sync source, and the others need to be set up to take that signal from it.

[bluebell]

The sync bit does bring to mind a caution: beyond the ADAT cable you use to hook the separate mic preamp unit (the Octopre, or something like a Behringer ADA8000) to your interface, you will also need a "clock sync" cable: it is likely that you need a separate, coaxial "word clock" cable: one of the devices (almost surely the interface) needs to be the "master" time sync source, and the others need to be set up to take that signal from it.

I have an ADA8200 connected with 2 optical cables (ADAT in/out) to my MOTU UltraLite AVB. There is no need for an additional sync cable. The ADA8200 gets synced via ADAT.

[autostatic]

Same here, Behringer ADA8200 with first gen RME Babyface, no extra cables needed besides the optical ones.

[tseaver]

@bluebell, @autostatic

Interesting. Given the OP's interest in the OctoPre, I checked its manual here:

https://fael-downloads-prod.focusrite.c ... -%20EN.pdf

The OctoPre can serve as the clock source master over ADAT (assuming that the interface allows it) but requires the separate BNC coax "word clock" cable to have the interface serve as the clock source master.

[bluebell]

@bluebell, @autostatic

Interesting. Given the OP's interest in the OctoPre, I checked its manual here:

https://fael-downloads-prod.focusrite.c ... -%20EN.pdf

The OctoPre can serve as the clock source master over ADAT (assuming that the interface allows it) but requires the separate BNC coax "word clock" cable to have the interface serve as the clock source master.

It can act as a clock source master via ADAT, see page 9. In this case a BNC cable is not needed. Sync via BNC is an alternative method.

[autostatic]

This is not necessary for the ADA8200, it gets synced over ADAT and the RME Babyface takes care of that.