Topic: Sound Devices MixPre-D to Raspberry Pi-2

[quiet-one]

Hi All,

I’m trying to install a Mixpre-D as the USB audio device on a Raspberry Pi-2 (Jessie). When I run the command “lsusb” it’s not on the list of devices. However, it shows up on ALSA mixer. Using the Nano editor, I wrote a .conf file to change the slot assignments so that that USB audio device is now the default device (=0) and the internal PCM card is now =1. However, ALSA mixer still has no control of the Mixpre. Also the Mixpre is still not showing on the RPi-2’s Preferences-Audio Device Settings. This technique is supposed to work for some USB sound devices. What am I missing? Does anyone know if the Mixpre will even operate on a RPi-2? I’m reading that not all USB sound cards will play nice with a Raspberry Pi. Sound Devices says that the Mixpre must operate in “full speed” mode when connected by USB to a Linux system. They instruct to hold the headphone knob down and reconnect the USB. RPi’s don’t seem to like devices to be hot-swapped. So maybe that’s the problem.

Further more, does anyone care to offer some tips on what I’m trying to accomplish. I make nature recordings, and I’ve been asked to lead “sound walks.” I would like for participants to hear my microphones on their cell phones by tapping into a live stream that I create and transmit with a portable WiFi access point (a LAN set for static IP). Participants would connect to my LAN and hear the live stream from a static web page as soon as they opened their browser. I can’t find an intermediary device between the Mixpre and the WiFi router, and a friend suggested that I build one with a Raspberry Pi-2. Of-course I have yet to find anyone who’s done this kind of thing before. Doing some research, it seems that a Raspberry Pi-2 could do an adequate job. I was reading that the WebRTC protocol is now on iOS devices and Android, and that the RPi -2 will operate as a UV4L server, so quality and latency should not be an issue.  Some basic requirements for the whole rig is: 1. that it must be small and easily powered by battery (4 hours max), 2. that it have only one function (power up and play - no monitor, keyboard or mouse required to initiate), 3. not require an internet connection (‘cause there won’t be one available out there), 4. participants not be required to install an app (‘cause that’s a pain in the ass, and too many of them will have trouble doing that anyway). I’m in over my head on this, but I like to learn about new things, so this seems like a fun and reasonable project. Any thoughts, tips, pitfalls to avoid, etc? Much appreciation in advance.

Fred

[rastasean]

Hi Fred,

wow, this is something else.

I would think lsusb is the right command to show when usb devices are connected. What's your dmesg report when you connect/disconnect the mixpre-d? I don't know if the mixpre-d will work on the raspberry pi 2. Do you have a x86 linux machine you can use to see if it will work?

For the second part. If the mixpre-d and raspberry pi2 works, you want users to be able to connect to your wifi access point and listen to the audio from your mics -->pre-amp --> raspberry pi?

Take a look at this video: https://www.youtube.com/watch?v=KI0LuIcFM98

He talks about using multicasting. That's essentially what you'll be doing...all the end points will be in a group and you may be able to broadcast to them. I don't know the likelihood of all of this being setup without any kind of access to the raspberry pi.

Test, test, test.

[quiet-one]

Hey Rastasean, thanks for the response. I think the situation is not as dire as I originally suspected. Using the speaker test command (speaker-test -D plughw:0,0 -c 2), I was able to hear a pink noise test pattern originating from the RPi and playing back on the MixPre Return input. All vial USB and heard on my headphones. So, there’s some type of connection going on.

I did the dmesg command after unplugging and plugging in the MixPre, here’s the report;
ck.
[ 2159.661824] usb 1-1.5: USB disconnect, device number 9
[ 2522.974263] usb 1-1.4: USB disconnect, device number 6
[ 2526.282277] usb 1-1.4: new high-speed USB device number 10 using dwc_otg
[ 2526.382994] usb 1-1.4: New USB device found, idVendor=0926, idProduct=0208
[ 2526.383025] usb 1-1.4: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[ 2526.383041] usb 1-1.4: Product: MixPre-D
[ 2526.383057] usb 1-1.4: Manufacturer: Sound Devices
[ 2526.383072] usb 1-1.4: SerialNumber: JP0613156005
[ 2526.385946] usb 1-1.4: 1:3 : UAC_AS_GENERAL descriptor not found
[ 2526.393771] hid-generic 0003:0926:0208.0004: hiddev0,hidraw2: USB HID v1.01 Device [Sound Devices MixPre-D] on usb-3f980000.usb-1.4/input3

One of the things that I learned is that the ALSA mixer does not have controls for all USB audio devices. Perhaps the MixPre-D is one of those devices. I guess next to do is a test record, listen and determine the file attributes.

Thanks,
Fred

[if_then_else]

The MixPre-D works on Ubuntu / Mint / Debian. It's a USB class compliant device and as such supported by the Linux kernel. But you'd probably want to use JACK (instead of Pulse or ALSA).