Should I buy a Scarlett 18i8

Looking for some advice here. I previously bought the wrong interface and I realized I could have saved myself some trouble if I had asked first.

I’m looking at buying a four input Focusrite Scarlett 18i8. I’m currently running Ardour-8.1.0 on Linux Mint 21. What I want to do is plug a guitar, mic, and Roland electronic drum set into three of the four inputs and record them on three separate tracks. Maybe later a bass on the fourth track.

I’m just hoping to find out if there are any potential issues with the Scarlett 18i8 with Ardour / Linux, or if there are any comments on whether this is a good choice or not.

If anybody has seen my last post finding-hardware-inputs – I’m not planning to try to use this together with my old Scarlett.

Appreciate any input anybody has!

Mostly depends if you’re intending to record mutiple tracks at once or susequently. For simultaneous recording you might want to get something with a DSP to take some load from bus and CPU. These interfaces unfortunately are not cheap.

That only reduces CPU load if you are trying to monitor the signal through the DAW with processing applied (e.g. compression or reverb), and the DSP in the interface has something close enough to what you want that it can be used, and it has a driver available which lets you use the DSP. That last part is often not available on Linux, so it is more common to just monitor the input signal dry using hardware monitor routing.


All right. I’ll dump all that useless RME crap from my studio then and live happily forever with onboard audio. As I did 20 years before. (The fact that any piece of hw should be supported by the underlying operating system aside.)
Unless, of course, I assume that you don’t really know how multichannel audio gets on the bus and what a DSP actually does - handling DSP effects is not it’s primary job (unless you believe in Wave’s marketing trying to sell you networked CPUs as “DSP grid” to run their 100% CPU-based plugins).

If you only need 4 inputs, consider the Behringer UMC404HD. The Focusrite 8i8 actually has 8 inputs, as it also has line-in inputs on the back. But if you don’t need them, then why pay for them.

I’ve used the Behringer UMC204HD and it was rock solid for me under Linux, and in some tests I have seen it outperforms the Focusrite Scarlett equivalent (although Focusrite have recently released a new series which claims better noise floor).

If you do need more inputs, then consider the Behringer UMC1820 which has 18 inputs and 20 outputs and is still cheaper than the Focusrite 8i8. I know someone who has one of these and swears by it.

Another thing to consider: although these audio interfaces are “consumer”, don’t mistake that with being poor quality. In many respects (resolution, noise floor, bandwidth), modern consumer audio interfaces are considerably better than anything even the best recording studios in the world had in the 1960s and 1970s.




Of course long time Linux audio users know that RME is one of the few vendors which does help get their devices supported on Linux. Many other vendors are not so helpful.

DSP is a very broad term, and when exposed to customers are part of a device marketing it typically refers to user selectable effects processing.

Of course any audio interface has to do bit shuffling to get onto the computer bus interface, and every modern converter is oversampling and includes DSP as an intrinsic part of operation, but you would never see those functions described as “DSP” on the box or when advertising features to customers.

Perhaps you were referring to input monitoring? That certainly could be implemented in DSP, but the devices I use implement that in the analog circuitry, so I would not generally assume that “DSP” as an interface feature meant input monitoring.

Perhaps it would be more useful if you gave concrete examples of what you are referring to instead of borderline rude responses without useful information.


Hi Mike,

it seems you don’t need 4 microphone preamps - if you do, nevermind my response :wink:

The mic needs a premap, and maybe the guitar (if recorded via mic), but the drumset and the bass can normally be plugged into a line-in input.

So if two microphone preamps and two additional line-inputs would be a solution, I can recommend the MOTU M4 which offers great quality for around 300 bucks. There are, of course, cheaper 4-in 4-out interfaces, but I use the MOTU M4 with Ardour under Linux and Windows on two different machines and it runs very well - no problems, nice sound quality, low latency.


I’m not an expert on this, so I would appreciate an explanation.

I completely understand how having DSP on the audio interface side to handle the bus processing could be beneficial (and RME interfaces have a reputation for low latency which, I presume, is related to this).

But I’m failing to understand how that outboard DSP which optimises the bus processing at the audio interface end benefits the CPU and bus on the PC, which just sees a stream of URBs without knowledge of whether they have been DSP processed or not.

Perhaps you could explain how this bus processing on the AI specifically benefits. the CPU loading of the PC.



The 2nd and 3rd generation 18i8 devices have received support from a user who has written a mixer application and submitted kernel patches to make them fully operational on Linux. In a thread on, he stated Focusrite reached out to him recently and is providing him some assistance to get more of their devices operating on Linux, so compatibility should not be a problem. Here is his project’s GitHub page:

I bought a UMC1820 in 2017, enjoy using it as my desktop’s primary soundcard as well as for recording, and have had no issues with it. The UMC404HD is the same device with fewer inputs and outputs. I actually like that there is no additional software needed, making its setup simple and essentially future-proof. If the internal routing of the Scarlett 18i8 is something you would find useful, that is an advantage of that device and the main reason for the mixer application. I have never owned one, but a number of people on forums have spoken positively of them over the years.

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Hi Mike,

My 18i8 (2nd gen) works great and is complete overkill for my (or your stated) needs, but hey room to grow, I always say.

1.) On the Roland Modules I’m familiar with, the Master Outs (assuming there are 2) can go to Line Inputs on the back of the Scarlet 18i8, 8i6 or 4i4 and that will record audio from your drumkit either on a stereo track or two mono tracks, or to a single mono track from the Left Master Out.

2.) You can run your guitar direct into one of the 1/4"/XLR Combo jacks on the front and set it to Inst in software (thanks to Geoffrey Bennett as mentioned by @GuntherT ) (The 4th gen solo and 2i2 got rid of the combo jacks and put the instrument ins on the back, so that can be a bit confusing)

3.) Run your mic (for vocals or mic’ing an amp) into one of the Combo jacks on the front (you’ll need to hit the 48V phantom power button if you’re using a condenser mic, not for a dynamic)

If you want to add a bass guitar later, you can always unplug your guitar. Contrary to the suggestion by @roax1, I really don’t think you’d want to plug your bass directly into a line-in on the back of the Focusrites. If you have a DI box or an amp with a line output, then fine, but not direct. I’d be happy to be proven wrong.

The Scarlett 4i4 and 8i6 will do all that, plus both have MIDI input in case you want to use your drumkit to play drum plugins down the line.

If you REALLY don’t want to swap cables between your guitar and your bass (or maybe bring someone in to play with you), then yes, a 18i8 will handle that.

FYI, through the Focusrite website (in the US at least), you can usually get previous generation or refurbished units at a discount. My refurb has been rock solid.

Good luck,

PS-I’m running Mint 21 as well

I agree to the bass DI/line-out, I was just telling the short version that you could probably use a line-in for your bass recording and not a mic preamp.

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Maybe could get away with that if the bass has active pickups, but not for traditional passive magnetic pickups, definitely need an instrument input for those to sound right.

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First off, many thanks to everyone who responded!

Keith, I am now considering the UMC404HD instead of the Focusrite. The Behringer has just what I was looking for, four inputs that I can plug in either guitar, mics, or line inputs.

I now realize, that if I go with the Scarlett I should get the 4i4, which has two line inputs in the back. But it seems like having four “universal” inputs would be more flexible.

Keith, do you happen to know if there’s a full user manual for the UMC404HD available? I looked around on the Behringer site, but I was only able to find a “quickstart guide.”

Thanks again Keith – and everyone.

Manuel, thanks so much for this detailed response. I missed the fact that there were line inputs on the back of the 4i4. I also didn’t realize I could still buy the 3rd gen, but when I search for them, there they are! I’m actually thinking about the Behringer that Keith suggested now, but haven’t decided for sure. This is a valuable learning process for me.

Yep. I also have one of these here.

The only initial “flaw” I had was input 3 and 4 being silent. After trying out some things I eventually opened up alsamixer and saw, that the fader for “Mic Rear” (AFAIR) was down to 0. After moving it up like “Mic Front” and keeping sure that the “CAPTURE” flag was enabled, all 4 inputs were ready to go. Works like a charm since then…

So far I only know one use case, where I would NOT recommend the Behringer UMCs: if you want to hook up one of the outputs to a guitar amp using a medium to high gain/distortion setting (with the goal to record the “playback” with a microphone pointing to the cabinet). For this case the UMC’s output just has too much noise on it.
PS: I didn’t have the chance yet to try this use case with a Focusrite Scarlett 2i2 (3rd gen) - the interface that my band singer has. So I can’t tell, whether it’s better, same, or worse…



I wanted to pop in to say I also have the UMC404HD, and it’s been great with Ardour on my Linux (Ubuntu Studio). Worked immediately, has been solidly working for years, and I typically run simultaneously record on all four channels at once and I’ve been very happy with it. Quality was a HUGE jump up from my old AVID M2.

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I believe the quick start manual is all there is. I’m not sure what else could be put in a larger manual: these are pretty straightforward devices.



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There is some more info in the Julian Krause review of the Behringer 404HD. In particular, a few diagrams explaining the difference between the different output options and the “Monitor A/B” button.

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Thanks Andreas, it hadn’t occurred to me how many people were reviewing these things on YT, but it appears that there is a wealth of information there!

Yes, but note that most “reviews” of audio interfaces on YouTube are just unboxing and someone reading the specs from the product web pages. Julian Krause is different. He makes relevant measures to check if the specs are actually true, and has a good idea about what is relevant and not.

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