Please recommend a Linux-friendly audio interface with hardware loopback

I need a self-powered and portable USB audio interface with two analog inputs and a hardware loopback. And it must be supported OOTB in Linux. The loopback requirement is what has tripped me up so far.

Regarding the loopback, it could be done via 1) a software mixing/routing application that runs on Linux [and can save the routing configuration to hardware] or 2) via connecting a cable from a digital output to a digital input. (Obviously, I would prefer choice 1.)

In addition to the loopback, I need two analog inputs with decent mic preamps.

I have a Scarlett 6i6 and I can create the loopback via a cable from SPDIF out to SPDIF in.

But the 6i6 isn’t recognized by PulseAudio at all (unlike the 2i2, for example). Since I just bought the 6i6 and I have 30 days to return it, I want to find a better device for Linux. And many people say there are better mic preamps in other devices, so I’m ready to make a switch.

I would consider anything from the Roland QuadCapture to the RME Babyface or really anything that meets the requirements I listed above. I’m new to this so I don’t have the experience to figure this out on my own. I can read the specs on those devices but I can’t figure out from the specs if they will actually do what I’m trying to do.

So far I have bought a Scarlett 2i2 then traded it for the 6i6 and neither works. (Actually, the 6i6 does do what I need, it just doesn’t do it on Linux. So I can’t use it.)

Can anyone offer a list of portable USB devices with 2 analog inputs and a hardware loopback? Thanks

what do you mean by loopback?

Do you mean that you need to run jack all the time and allow non jack programs to be able to play through your hardware?

If thats the case, this is done and already setup for you in a few distrubutions of linux. KX studio has it all setup and running out of the box, you just need to configure jack to use your interface and make sure that once you restart jack that also loop gets started aswell.

AV linux also does this, it doesnt start at boot automatically, theres a script you run which is in one of the menus in av linux.

Alot of people recomend not using pulse at all for a good linux audio setup for mixing. Stick with alsa and jack.

i use a 18i6 and it works great with DreamStudio, just press start jack once the system is up, in the worst case would need to press also “start pulse-jack”, all this is under a button on the user interface, top left of the screen, jack logo.

I’m pretty sure that dsus means what most of us call “hardware monitoring” - looping back incoming signal to the device’s output, without hitting the CPU.

I have a Komplete Audio 6 and it works fully out of the box on Linux. I only tested it in detail with Jack but pulseaudio seems also happy with it. Nearly all controls are accessible through hardware buttons and the only one which isn’t (spdif clock source) can be set through alsamixer. It has harware monitoring and spdif in/out. The preamps are very good (actually better to my ears than those of the Scarlett 2i4 which I tried before).

Thanks for all the replies. (I wasn’t notified of the replies – I’ll have to check my settings here.) What I mean by loopback is like the routing feature available in higher end Focusrite products and probably many others on the market. In Focusrite products it is called loopback in the Mix Control. (It is also called loopback when done via alsa modules, but I am new to all this and I don’t know what most people call this functionality.) From what I have seen on some hardware any output can be routed back to an input. I need this feature in a smaller interface.

If I wanted to pick one of the higher end Focusrite products and I could find one that would work on Linux, then that would be a solution. I would use the mix control software, set up my loopback and then save it to hardware. Done. I just want a smaller portable USB interface that works with Linux, yet has this loopback feature.

So far someone has confirmed that the RME Babyface has this feature. It can be done via the mix control software or via a physical cable. That’s just what I was looking for. However, I’m told that the Babyface has trouble with current alsa drivers. My alsa driver is 1.0.25. Apparently this driver has a bug that affects audio interfaces (and other devices). I did not find any online reports of the Babyface working in Linux due to this driver bug.

BTW, I need this loopback feature because I’m trying to record the output of software along with analog input to the audio interface. It sounds really simple. But I have been stymied in my attempts to find a solution.

Basically, I just need two analog inputs, two TS outputs and a loopback that will send input from software on my computer back to a recording application on my computer (along with the signals from the two analog inputs). I want to record each input on its own track.

Again, it seems simple enough. And I can do it easily on a Mac. I can also do it in Linux with JACK. But I want a hardware device that can do it so I can just plug it into almost any Linux box and it will work (without me having to remove PulseAudio or deal with Jack vs PA conflicts and things like that). I have to use this on a muti-purpose computer and I am very hesitant to remove PulseAudio or install Jack. So I’m looking for a hardware based solution. Again from what I have been told the Babyface would be ideal if not for the current alsa driver bug.

As I’m learning more about this I’m not sure there is a pure hardware solution at the moment due to the driver bug. Maybe I just need to get more comfortable with Jack and take a chance using it on my multi-purpose machine. (BTW, this is all for podcasting.)

@svictor - do you have the problem with cracks and pops in your Komplete Audio 6? Many reviewers on Amazon.com mention this issue. Otherwise, the device looks very interesting. Is there a way to set up routing in the device and save it to hardware? (If not, I guess I could use a cable from SPDIF out to in).

BTW, these two video tutorials show the loopback routing feature I’m asking about:


In these higher end Focusrite products, you can set up the loopback in the mix control then save that routing configuration to the hardware. That way, once set, the device can be used on Linux without the mix control software.

@dsus: Yes i understand now what you´re talking about, i have both the Saffire Pro 40 and the Scarlett 18i6, the Scarlett doesn´t have a “loopback” function which is hardware based, this is: “a non-physical input fed with the user´s choice in the Saffire Control Mixer” which in the case you´re talking about is a mix of several things.

So i have a couple of thoughts about it:

  1. Although the Scarlett series are very good hardware pieces they do not support this feature which wont be of course recognized back in Jack and Ardour, or Protools for that matter.
  2. You say that “what you want to do” is record a software output along with analog input, if i´m correct, thas very easily done with Jack, and you can record each source to a different track which you can mix back together later for better results
  3. Jack has the ability to store and restore “sessions” that you have worked with before and thus have the connections already made right, i don´t use that feature but it exists and in this case you should read a bit about it and play with it a lot more until you get it right and to do what you need.
  4. Having read points 1, 2 and 3: there´s no need to spend on hardware but instead would be wise to spend a little more time on researching and tweaking, may not be the easiest way but i believe is worth the effort, you´ll see, what takes you 3 minutes to set up today maybe later with the proper knowing will take you less than 1 minute and i´ve come to value that since almost every recording setup i do is more or less different.

Sorry for the bad english

The jack sound server is basically a virtual patch bay. It means you can route any jack aware program to any other jack aware program.

And if a program isnt jack aware, you can use a software loopback. In kx studio this is already setup, Jack is always running, and any non jackaware programs use alsa which get routed through jack through an alsa/jack bridge. So, i could route something playing through my browser into ardour or another recording program. or any other program for tha matter that doesnt support jack.

Also with jack i could have a softsynth loaded up and route its output into a DAW of my choice for recording.

Im not sure if hardware loopback would ever be required.

Also now that were talking about session management, also in kx studio there is a great setup that allows you to setup and store session, you can even create virtual studios with virtual rooms, and have different patches stored for different projects. It has cadence which is for configuring jack and the alsa jack bridges, and it has links from there to carla and cadence for session management, and some other nifty tools.

The only problem i have with kx studio is that it seems to be more resource intensive than av linux, running at 2ms latency on kx studio i use alot of DSP with just a few fx compared with the same 2ms latency on av linux, but kx studio seems to be set up much nicer in terms of utilities like cadence and carla, and catanio

@dsus: no cracks and pops for me :slight_smile: I also read such comments before buying the card, but I supposed that the problems were linked to the drivers on Win/Mac. Some people say they are buggy… The description also sounded like a typical latency problem (xruns). This kind of thing is easyer to solve on Linux, as you can change the kernel and other things. I use the card on both Ubuntu (generic kernel) and Arch (realtime kernel) with no problem.

There is no way to set routing in the KA6 hardware. SPDIF out to in should work (I didn’t try it).

Actually, understanding what you’re looking for, I remember that my previous card had a hardware loopback feature. It was an Edirol UA-25. It used to be quite popular amongst linux musicians because it worked out of the box (and it was cheap and very solid). Past tense because it’s not produced anymore. But if you can find one second hand, you could consider it.

I have M-Audio Fast Track Ultra, which has an internal routing feature. I can control that in alsamixer. It has 8 inputs, and one can mix them to two stereo headphone outputs. In addition of that, one can mix also 8 software return channels from computer to those same two stereo headphone outputs. I wrote (long and boring) post about that: http://heikki.ketoharju.info/2013/03/linux-and-fasttrackultra/

Fast Track Ultra works with regular Alsa drivers, and you could also carry the right settings with you as asoundrc-file. Am I correct?