[Portaudio] using all channels of class compliant RME Babyface Pro USB audio interface

Be be.0 at gmx.com
Thu Dec 10 01:37:01 EST 2015


Hello, I just got an RME Babyface Pro USB sound card. It can operate 
either as a USB audio class compliant device (with mixing controlled by 
the device's physical controls) or make use of a proprietary driver on 
Windows and Mac OS X. I am trying to use its class compliant mode to use 
with Mixxx for DJing on GNU/Linux. However, I cannot figure out how to 
use channels 3-4 for my headphones. The device has 4 analog channels out 
and in plus 8 digital out and in (via ADAT). Its manual says, regarding 
class compliant mode, "in Mac OS X, either the first two or all channels 
will work, depending on the choice in the Audio MIDI Setup." I believe 
the two channel operation exists so when the Babyface Pro is plugged 
into an iPad, the iPad sends stereo output from iTunes and other 
programs to the Babyface Pro's main output. However, I do not know how 
to select between this 2 channel mode and the 12 channel mode with 
Linux. PulseAudio only shows it as a stereo device. Mixxx, which uses 
PortAudio, displays all 12 channels as available but doesn't work when 
any channels other than 1-2 are selected. Here is debugging output of Mixxx:

Debug [Main]: SoundManager::setupDevices()
Debug [Main]: SoundDevicePortAudio::open() "2, Babyface Pro (70785713): 
USB Audio (hw:1,0)"
Debug [Main]: framesPerBuffer: 256
Debug [Main]: Requested sample rate:  44100 Hz, latency: 5.80499 ms
Debug [Main]: Output channels: 4 | Input channels: 0
Debug [Main]: Opening stream with id 2
Expression 'alsa_snd_pcm_hw_params_set_channels( pcm, hwParams, 
self->numHostChannels )' failed in 'src/hostapi/alsa/pa_linux_alsa.c', 
line: 2051
Expression 'PaAlsaStreamComponent_InitialConfigure( &self->playback, 
outParams, self->primeBuffers, hwParamsPlayback, &realSr )' failed in 
'src/hostapi/alsa/pa_linux_alsa.c', line: 2717
Expression 'PaAlsaStream_Configure( stream, inputParameters, 
outputParameters, sampleRate, framesPerBuffer, &inputLatency, 
&outputLatency, &hostBufferSizeMode )' failed in 
'src/hostapi/alsa/pa_linux_alsa.c', line: 2838
Warning [Main]: Error opening stream: Invalid number of channels

aplay -l output:
**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC272 Analog [ALC272 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
card 0: PCH [HDA Intel PCH], device 3: HDMI 0 [HDMI 0]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
card 1: Pro70785713 [Babyface Pro (70785713)], device 0: USB Audio [USB 
Audio]
   Subdevices: 1/1
   Subdevice #0: subdevice #0

aplay -L output:
null
     Discard all samples (playback) or generate zero samples (capture)
pulse
     PulseAudio Sound Server
default
     Default ALSA Output (currently PulseAudio Sound Server)
sysdefault:CARD=PCH
     HDA Intel PCH, ALC272 Analog
     Default Audio Device
front:CARD=PCH,DEV=0
     HDA Intel PCH, ALC272 Analog
     Front speakers
surround21:CARD=PCH,DEV=0
     HDA Intel PCH, ALC272 Analog
     2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=PCH,DEV=0
     HDA Intel PCH, ALC272 Analog
     4.0 Surround output to Front and Rear speakers
surround41:CARD=PCH,DEV=0
     HDA Intel PCH, ALC272 Analog
     4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=PCH,DEV=0
     HDA Intel PCH, ALC272 Analog
     5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=PCH,DEV=0
     HDA Intel PCH, ALC272 Analog
     5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=PCH,DEV=0
     HDA Intel PCH, ALC272 Analog
     7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
hdmi:CARD=PCH,DEV=0
     HDA Intel PCH, HDMI 0
     HDMI Audio Output
sysdefault:CARD=Pro70785713
     Babyface Pro (70785713), USB Audio
     Default Audio Device
front:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     Front speakers
surround21:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     2.1 Surround output to Front and Subwoofer speakers
surround40:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     4.0 Surround output to Front and Rear speakers
surround41:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     4.1 Surround output to Front, Rear and Subwoofer speakers
surround50:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     5.0 Surround output to Front, Center and Rear speakers
surround51:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     5.1 Surround output to Front, Center, Rear and Subwoofer speakers
surround71:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     7.1 Surround output to Front, Center, Side, Rear and Woofer speakers
iec958:CARD=Pro70785713,DEV=0
     Babyface Pro (70785713), USB Audio
     IEC958 (S/PDIF) Digital Audio Output

/proc/asound/card1/stream0 when playing to channels 1-2 with PulseAudio:
RME Babyface Pro (70785713) at usb-0000:00:1d.0-1.2, high speed : USB Audio

Playback:
   Status: Running
     Interface = 1
     Altset = 1
     Packet Size = 47
     Momentary freq = 44118 Hz (0x5.83c9)
     Feedback Format = 16.16
   Interface 1
     Altset 1
     Format: S24_3LE
     Channels: 2
     Endpoint: 3 OUT (ASYNC)
     Rates: 44100, 48000, 88200, 96000, 176400, 192000
     Data packet interval: 125 us
   Interface 1
     Altset 2
     Format: S24_3LE
     Channels: 12
     Endpoint: 3 OUT (ASYNC)
     Rates: 44100, 48000, 88200, 96000, 176400, 192000
     Data packet interval: 125 us

Capture:
   Status: Stop
   Interface 2
     Altset 1
     Format: S24_3LE
     Channels: 12
     Endpoint: 4 IN (ASYNC)
     Rates: 44100, 48000, 88200, 96000, 176400, 192000
     Data packet interval: 125 us
   Interface 2
     Altset 2
     Format: S24_3LE
     Channels: 2
     Endpoint: 4 IN (ASYNC)
     Rates: 44100, 48000, 88200, 96000, 176400, 192000
     Data packet interval: 125 us

So I guess the question is how to get PortAudio to use the "Altset 2" 
option. Could this be accomplished with some asoundrc sorcery? Does 
something need to change in snd-usb-audio? Is the issue with PortAudio 
and PulseAudio? How can I test channels 3-4 with aplay or another program?


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