External DAC / sound card in OpenBSD

[Os Miridium]

Hi there,

fairly recent OpenBSD convert here after a decade on linux. I must say I am pleasantly surprised how often I can just do what "feels like it should work" and it actually works. Nice. However, I still have some things to work out.

I am now trying to connect a Focusrite Scarlett 2i4 USB DAC to my OpenBSD system to use as an external sound card. From what I have figured out so far, it seems I need to point an audio "device" (probably audio1) at the one of the stereo output channels of the Scarlett. If I understand these two correctly, the interface should show up in dmesg as connected to audio1 with a line like:

audio1 at uaudio0

There is no such line in my dmesg. It seems like this might/should happen automatically or can be done manually. My question is, how do I make it so?

Here is my $ dmesg | grep audio

audio0 at azalia1
uaudio0 at uhub0 port 4 configuration 1 interface 0 "Focusrite Scarlett 2i4 USB" rev 2.00/1.25 addr 3
uaudio0: audio descriptors make no sense, error=4
uaudio1 at uhub0 port 4 configuration 1 interface 3 "Focusrite Scarlett 2i4 USB" rev 2.00/1.25 addr 3
uaudio1: audio descriptors make no sense, error=4
uaudio0 detached
uaudio1 detached
uaudio0 at uhub0 port 4 configuration 1 interface 0 "Focusrite Scarlett 2i4 USB" rev 2.00/1.25 addr 3
uaudio0: audio descriptors make no sense, error=4
uaudio1 at uhub0 port 4 configuration 1 interface 3 "Focusrite Scarlett 2i4 USB" rev 2.00/1.25 addr 3
uaudio1: audio descriptors make no sense, error=4

azalia1 being the internal sound card.

I did not find a solution (or did not recognize it as the solution) in the man pages of sndio, sndiod, audio, audioctl, or mixerctl. Where else did I miss to look?
Any help would be greatly appreciated.

Thanks,
Os

[ibara]

First thing to check: is this connected to a USB 3.0 port? uaudio doesn't work on USB 3.0 ports (yet); connect it to a USB 2.0 port if you can.

[Os Miridium]

Ah, that is mighty good to know! It is indeed connected to a USB 3.0 port. I cannot right now but I'll check what happens when switching it over to a 2.0 port as soon as I can tomorrow and report back.

Thanks,
Os

[Os Miridium]

Now I moved the DAC over to a USB 2.0 port. Still no

audio1 at uaudio0

Here is the new $ dmesg | grep audio

audio0 at azalia1
uaudio0 at uhub3 port 5 configuration 1 interface 0 "Focusrite Scarlett 2i4 USB" rev 2.00/1.25 addr 2
uaudio0: audio descriptors make no sense, error=4
uaudio1 at uhub3 port 5 configuration 1 interface 3 "Focusrite Scarlett 2i4 USB" rev 2.00/1.25 addr 2
uaudio1: audio descriptors make no sense, error=4

I do have the /dev/audio1 file, so that can't be it. This is my $ ls /dev | grep audio

audio
audio0
audio1
audio2
audioctl
audioctl0
audioctl1
audioctl2

The Midi-section of the Multimedia FAQ mentions that

The output of the keyboard can be connected to the input of the synthesizer, as follows:

$ cat -u < /dev/rmidi0 > /dev/rmidi1

I have a shadow of an inkling that that may be the method of connecting the device that I am looking for. If so, then the question is: Which file do I cat into which?

Thanks,
Os

[Paianni]

You are trying to use a Class 2 USB Audio (UAC2) device, and these aren't supported in OpenBSD, only UAC1. A popular UAC1 device with a combined DAC/ADC is the Behringer UCA200/202/222, but there are also separates like the ODAC rev. B and Altor's experimental Olivine ADC.

[Os Miridium]

@Paianni
Ah, now that sounds like it may solve my problem, thanks!

A quick sifting through some USB info seems to suggest that the UAC standard numbers are tied to the general USB standard releases, meaning all USB 1.x devices should have UAC1, all USB 2.x devices should be UAC2 etc. Can anyone confirm ore refute that? If my assumption is correct that would mean I should be able to use a Behringer Xenyx 302 USB, which seems to be USB 1.1 (according to a customer review complaining about this fact, although the manufacturer does not bother to say so anywhere in the obtainable official info) . Has anyone by any chance thried this particular device? It does have a few handy features that the UCA2xx series is missing.

Thanks again,
Os

[Paianni]

Originally Posted by Os Miridium

@Paianni
Ah, now that sounds like it may solve my problem, thanks!

A quick sifting through some USB info seems to suggest that the UAC standard numbers are tied to the general USB standard releases, meaning all USB 1.x devices should have UAC1, all USB 2.x devices should be UAC2 etc. Can anyone confirm ore refute that? If my assumption is correct that would mean I should be able to use a Behringer Xenyx 302 USB, which seems to be USB 1.1 (according to a customer review complaining about this fact, although the manufacturer does not bother to say so anywhere in the obtainable official info) . Has anyone by any chance thried this particular device? It does have a few handy features that the UCA2xx series is missing.

Thanks again,
Os

Yes, if an audio device is listed as USB 1.1 compliant in the specifications, it will almost certainly work. However, most of them don't support 24-bit quantisation, which is kinda important for studio recording.

[Os Miridium]

@ Paianni

Yes, if an audio device is listed as USB 1.1 compliant in the specifications, it will almost certainly work. However, most of them don't support 24-bit quantisation, which is kinda important for studio recording.

Thanks! Of course the manufacturer does not tell us that it is USB 1.1 compliant, just that it is a USB interface. But since they fail to bragg about being USB 2.0, it seems likely enough to me to be 1.1 to justify ordering the thing and giving it a try. I'll report back on success or failure.

Indeed the Behringer Xenyx 302 USB is 16-bit @ 48 kHz, so indeed not what most people would consider "studio quality". But since I need the thing mainly as a flexible audio output device (D to A) for home entertainment purposes that is not too big a concern to me. I might use it for some quick sketching of musical ideas, but the fact that OpenBSD does not support USB 2.0 audio means that my Linux machine together with the rather good sounding Focusrite interface will remain my actual recording station for the time being.

Best Regards,
Os

[ibara]

This may help get your audio device working:
https://marc.info/?l=openbsd-tech&m=154627230907954&w=2

[new2BSDlol]

Originally Posted by Paianni

ODAC rev. B

Very interesting, and it has been updated https://blog.jdslabs.com/2017/04/odac-vs-ol-dac/

[ibara]

USB audio devices may work on USB 3.0 ports now:
https://marc.info/?l=openbsd-cvs&m=155269204722555&w=2

(This commit will make 6.5)

[new2BSDlol]

Support for USB audio is being upgraded from Class 1 to Class 2 in 6.5 as well... https://www.openbsd.org/65.html

uaudio(4) has been replaced by a new driver which supports USB audio class v2.0.

I bought an OL DAC to use with OpenBSD because it uses USB Audio Class 1... but I don't regret it, it sounds great compared to my motherboard audio and supports up to 96kHz sample rate which is plenty.