Focusrite Scarlett on Linux input mapping?

Question

Does anyone use these interfaces on Linux? If so, how do the inputs map (e. g. with ALSA/PulseAudio)?

E. g. the Scarlett 6i6 has the following connections.

Inputs:

• 2x symmetric XLR inputs (one for each channel)
• 2x symmetric phone connector inputs (one for each channel)
• 1x coaxial SPDIF input (stereo signal over a single wire)

Outputs:

• 4x symmetric phone connector output
• 1x coaxial SPDIF output (stereo signal over a single wire)

Each input has its own ADC and each output has its own DAC, so there's nothing that goes "through" to another channel.

Now my question is: How does this map onto audio channels under Linux?

1. Output-wise: Is it recognized as a single 6-channel card, so e. g. phone connector 1 is "front left", phone connector 2 is "front right", phone connector 3 is "rear left", phone connector 4 is "rear right", SPDIF channels are front and LFE or similar, "awkward" situation? Or is it recognized as three separate stereo audio cards? Or is even each output a single mono audio card? Or how?

2. Input-wise: Do the 2x symmetric XLR inputs form a "stereo pair", so that when I plug a microphone into one, then record, I only get signal on, say, left channel, and the right one is silent? Or do they act as two separate mono inputs? What with the other inputs?

Would be great if someone had this interface running under Linux and could give me some insights. I plan plugging a condenser mic into the interface via XLR and would be interested if the two XLRs act as a "stereo input" and when I record, I get signal on one channel but not on the other or how this would turn out.

Answer 1

The way I use my Focusrite 6i6, I use jack/alsa as the backend, and plug pulseaudio into jack to play audio from applications that don't natively support jack.

All of the input/output ports are totally configurable in alsamixer. This hardware was designed with a very malleable hardware mixer to be controlled by software, and although Focusrite doesn't support linux, someone did figure out how to communicate with the device and implement this functionality through the Scarlett 6i6's alsa driver.

Right now, I see 12 playback ports on the Scarlett, and 6 capture ports. The capture ports are configurable in alsamixer, although they could line up to the four analog inputs + two SPDIF channel inputs, the user is free to do what they will. The playback ports as well as the monitor and headphone outputs are also totally configurable through alsamixer (ie, you can set playback ports 7,8 and 11,12 to play back through the monitor as a stereo mix and set playback ports 1,2 and 3,4 to play back through headphones as a different stereo mix). Pulseaudio plays normal system sounds back smoothly over the Scarlett through the jack interface, although the Scarlett does not even show up for output through Pulseaudio.

I'm not sure how alsa works with stereo vs mono channels, but in jack, it's natural to think of a stereo channel as made up of two mono channels. I'm not sure whether alsa works the same way, but I would expect that you would have to mix the input channels into stereo yourself. I absolutely recommend jack with alsa backend and alsamixer to utilize & control this audio interface on linux, as the device would be almost crippled without control over the hardware mixer functions.