1        Guide to using M-Audio Audiophile USB with ALSA and Jack        v1.5
   2        ========================================================
   4            Thibault Le Meur <>
   6This document is a guide to using the M-Audio Audiophile USB (tm) device with 
   7ALSA and JACK.
  11* v1.4 - Thibault Le Meur (2007-07-11)
  12 - Added Low Endianness nature of 16bits-modes
  13   found by Hakan Lennestal <>
  14 - Modifying document structure
  15* v1.5 - Thibault Le Meur (2007-07-12)
  16 - Added AC3/DTS passthru info
  191 - Audiophile USB Specs and correct usage
  22This part is a reminder of important facts about the functions and limitations 
  23of the device.
  25The device has 4 audio interfaces, and 2 MIDI ports:
  26 * Analog Stereo Input (Ai)
  27   - This port supports 2 pairs of line-level audio inputs (1/4" TS and RCA) 
  28   - When the 1/4" TS (jack) connectors are connected, the RCA connectors
  29     are disabled
  30 * Analog Stereo Output (Ao)
  31 * Digital Stereo Input (Di)
  32 * Digital Stereo Output (Do)
  33 * Midi In (Mi)
  34 * Midi Out (Mo)
  36The internal DAC/ADC has the following characteristics:
  37* sample depth of 16 or 24 bits
  38* sample rate from 8kHz to 96kHz
  39* Two interfaces can't use different sample depths at the same time.
  40Moreover, the Audiophile USB documentation gives the following Warning:
  41"Please exit any audio application running before switching between bit depths"
  43Due to the USB 1.1 bandwidth limitation, a limited number of interfaces can be 
  44activated at the same time depending on the audio mode selected:
  45 * 16-bit/48kHz ==> 4 channels in + 4 channels out
  46   - Ai+Ao+Di+Do
  47 * 24-bit/48kHz ==> 4 channels in + 2 channels out, 
  48                    or 2 channels in + 4 channels out
  49   - Ai+Ao+Do or Ai+Di+Ao or Ai+Di+Do or Di+Ao+Do
  50 * 24-bit/96kHz ==> 2 channels in _or_ 2 channels out (half duplex only)
  51   - Ai or Ao or Di or Do
  53Important facts about the Digital interface:
  55 * The Do port additionally supports surround-encoded AC-3 and DTS passthrough, 
  56though I haven't tested it under Linux
  57   - Note that in this setup only the Do interface can be enabled
  58 * Apart from recording an audio digital stream, enabling the Di port is a way 
  59to synchronize the device to an external sample clock
  60   - As a consequence, the Di port must be enable only if an active Digital 
  61source is connected
  62   - Enabling Di when no digital source is connected can result in a 
  63synchronization error (for instance sound played at an odd sample rate)
  662 - Audiophile USB MIDI support in ALSA
  69The Audiophile USB MIDI ports will be automatically supported once the
  70following modules have been loaded:
  71 * snd-usb-audio
  72 * snd-seq-midi
  74No additional setting is required.
  773 - Audiophile USB Audio support in ALSA
  80Audio functions of the Audiophile USB device are handled by the snd-usb-audio 
  81module. This module can work in a default mode (without any device-specific 
  82parameter), or in an "advanced" mode with the device-specific parameter called 
  853.1 - Default Alsa driver mode
  88The default behavior of the snd-usb-audio driver is to list the device 
  89capabilities at startup and activate the required mode when required 
  90by the applications: for instance if the user is recording in a 
  9124bit-depth-mode and immediately after wants to switch to a 16bit-depth mode,
  92the snd-usb-audio module will reconfigure the device on the fly.
  94This approach has the advantage to let the driver automatically switch from sample 
  95rates/depths automatically according to the user's needs. However, those who 
  96are using the device under windows know that this is not how the device is meant to
  97work: under windows applications must be closed before using the m-audio control
  98panel to switch the device working mode. Thus as we'll see in next section, this 
  99Default Alsa driver mode can lead to device misconfigurations.
 101Let's get back to the Default Alsa driver mode for now.  In this case the 
 102Audiophile interfaces are mapped to alsa pcm devices in the following 
 103way (I suppose the device's index is 1):
 104 * hw:1,0 is Ao in playback and Di in capture
 105 * hw:1,1 is Do in playback and Ai in capture
 106 * hw:1,2 is Do in AC3/DTS passthrough mode
 108In this mode, the device uses Big Endian byte-encoding so that 
 109supported audio format are S16_BE for 16-bit depth modes and S24_3BE for 
 11024-bits depth mode.
 112One exception is the hw:1,2 port which was reported to be Little Endian 
 113compliant (supposedly supporting S16_LE) but processes in fact only S16_BE streams.
 114This has been fixed in kernel 2.6.23 and above and now the hw:1,2 interface 
 115is reported to be big endian in this default driver mode.
 118 * playing a S24_3BE encoded raw file to the Ao port
 119   % aplay -D hw:1,0 -c2 -t raw -r48000 -fS24_3BE test.raw
 120 * recording a  S24_3BE encoded raw file from the Ai port
 121   % arecord -D hw:1,1 -c2  -t raw -r48000 -fS24_3BE test.raw
 122 * playing a S16_BE encoded raw file to the Do port
 123   % aplay -D hw:1,1 -c2 -t raw -r48000 -fS16_BE test.raw
 124 * playing an ac3 sample file to the Do port
 125   % aplay -D hw:1,2 --channels=6 ac3_S16_BE_encoded_file.raw
 127If you're happy with the default Alsa driver mode and don't experience any 
 128issue with this mode, then you can skip the following chapter.
 1303.2 - Advanced module setup
 133Due to the hardware constraints described above, the device initialization made 
 134by the Alsa driver in default mode may result in a corrupted state of the 
 135device. For instance, a particularly annoying issue is that the sound captured 
 136from the Ai interface sounds distorted (as if boosted with an excessive high
 137volume gain).
 139For people having this problem, the snd-usb-audio module has a new module 
 140parameter called "device_setup" (this parameter was introduced in kernel
 141release 2.6.17)
 1433.2.1 - Initializing the working mode of the Audiophile USB
 145As far as the Audiophile USB device is concerned, this value let the user 
 147 * the sample depth
 148 * the sample rate
 149 * whether the Di port is used or not 
 151When initialized with "device_setup=0x00", the snd-usb-audio module has
 152the same behaviour as when the parameter is omitted (see paragraph "Default 
 153Alsa driver mode" above)
 155Others modes are described in the following subsections.
 1573.2.1.1 - 16-bit modes
 159The two supported modes are:
 161 * device_setup=0x01
 162   - 16bits 48kHz mode with Di disabled
 163   - Ai,Ao,Do can be used at the same time
 164   - hw:1,0 is not available in capture mode
 165   - hw:1,2 is not available
 167 * device_setup=0x11
 168   - 16bits 48kHz mode with Di enabled
 169   - Ai,Ao,Di,Do can be used at the same time
 170   - hw:1,0 is available in capture mode
 171   - hw:1,2 is not available
 173In this modes the device operates only at 16bits-modes. Before kernel 2.6.23,
 174the devices where reported to be Big-Endian when in fact they were Little-Endian
 175so that playing a file was a matter of using:
 176   % aplay -D hw:1,1 -c2 -t raw -r48000 -fS16_BE test_S16_LE.raw
 177where "test_S16_LE.raw" was in fact a little-endian sample file.
 179Thanks to Hakan Lennestal (who discovered the Little-Endiannes of the device in
 180these modes) a fix has been committed (expected in kernel 2.6.23) and
 181Alsa now reports Little-Endian interfaces. Thus playing a file now is as simple as
 183   % aplay -D hw:1,1 -c2 -t raw -r48000 -fS16_LE test_S16_LE.raw
 1853.2.1.2 - 24-bit modes
 187The three supported modes are:
 189 * device_setup=0x09
 190   - 24bits 48kHz mode with Di disabled
 191   - Ai,Ao,Do can be used at the same time
 192   - hw:1,0 is not available in capture mode
 193   - hw:1,2 is not available
 195 * device_setup=0x19
 196   - 24bits 48kHz mode with Di enabled
 197   - 3 ports from {Ai,Ao,Di,Do} can be used at the same time
 198   - hw:1,0 is available in capture mode and an active digital source must be 
 199     connected to Di
 200   - hw:1,2 is not available
 202 * device_setup=0x0D or 0x10
 203   - 24bits 96kHz mode
 204   - Di is enabled by default for this mode but does not need to be connected 
 205     to an active source
 206   - Only 1 port from {Ai,Ao,Di,Do} can be used at the same time
 207   - hw:1,0 is available in captured mode
 208   - hw:1,2 is not available
 210In these modes the device is only Big-Endian compliant (see "Default Alsa driver 
 211mode" above for an aplay command example)
 2133.2.1.3 - AC3 w/ DTS passthru mode
 215Thanks to Hakan Lennestal, I now have a report saying that this mode works.
 217 * device_setup=0x03
 218   - 16bits 48kHz mode with only the Do port enabled 
 219   - AC3 with DTS passthru
 220   - Caution with this setup the Do port is mapped to the pcm device hw:1,0
 222The command line used to playback the AC3/DTS encoded .wav-files in this mode:
 223   % aplay -D hw:1,0 --channels=6 ac3_S16_LE_encoded_file.raw
 2253.2.2 - How to use the device_setup parameter
 228The parameter can be given:
 230 * By manually probing the device (as root):
 231   # modprobe -r snd-usb-audio
 232   # modprobe snd-usb-audio index=1 device_setup=0x09
 234 * Or while configuring the modules options in your modules configuration file
 235   (tipically a .conf file in /etc/modprobe.d/ directory:
 236       alias snd-card-1 snd-usb-audio
 237       options snd-usb-audio index=1 device_setup=0x09
 239CAUTION when initializing the device
 242 * Correct initialization on the device requires that device_setup is given to
 243   the module BEFORE the device is turned on. So, if you use the "manual probing"
 244   method described above, take care to power-on the device AFTER this initialization.
 246 * Failing to respect this will lead to a misconfiguration of the device. In this case
 247   turn off the device, unprobe the snd-usb-audio module, then probe it again with
 248   correct device_setup parameter and then (and only then) turn on the device again.
 250 * If you've correctly initialized the device in a valid mode and then want to switch
 251   to  another mode (possibly with another sample-depth), please use also the following 
 252   procedure:
 253   - first turn off the device
 254   - de-register the snd-usb-audio module (modprobe -r)
 255   - change the device_setup parameter by changing the device_setup
 256     option in /etc/modprobe.d/*.conf
 257   - turn on the device
 258 * A workaround for this last issue has been applied to kernel 2.6.23, but it may not
 259   be enough to ensure the 'stability' of the device initialization.
 2613.2.3 - Technical details for hackers
 263This section is for hackers, wanting to understand details about the device
 264internals and how Alsa supports it.
 2663.2.3.1 - Audiophile USB's device_setup structure
 268If you want to understand the device_setup magic numbers for the Audiophile 
 269USB, you need some very basic understanding of binary computation. However, 
 270this is not required to use the parameter and you may skip this section.
 272The device_setup is one byte long and its structure is the following:
 274       +---+---+---+---+---+---+---+---+
 275       | b7| b6| b5| b4| b3| b2| b1| b0|
 276       +---+---+---+---+---+---+---+---+
 277       | 0 | 0 | 0 | Di|24B|96K|DTS|SET|
 278       +---+---+---+---+---+---+---+---+
 281 * b0 is the "SET" bit
 282   - it MUST be set if device_setup is initialized 
 283 * b1 is the "DTS" bit
 284   - it is set only for Digital output with DTS/AC3
 285   - this setup is not tested
 286 * b2 is the Rate selection flag
 287   - When set to "1" the rate range is 48.1-96kHz
 288   - Otherwise the sample rate range is 8-48kHz
 289 * b3 is the bit depth selection flag
 290   - When set to "1" samples are 24bits long
 291   - Otherwise they are 16bits long
 292   - Note that b2 implies b3 as the 96kHz mode is only supported for 24 bits 
 293     samples
 294 * b4 is the Digital input flag
 295   - When set to "1" the device assumes that an active digital source is 
 296     connected 
 297   - You shouldn't enable Di if no source is seen on the port (this leads to 
 298     synchronization issues)
 299   - b4 is implied by b2 (since only one port is enabled at a time no synch 
 300     error can occur) 
 301 * b5 to b7 are reserved for future uses, and must be set to "0"
 302   - might become Ao, Do, Ai, for b7, b6, b4 respectively
 305 * there is no check on the value you will give to device_setup
 306   - for instance choosing 0x05 (16bits 96kHz) will fail back to 0x09 since 
 307     b2 implies b3. But _there_will_be_no_warning_ in /var/log/messages
 308 * Hardware constraints due to the USB bus limitation aren't checked
 309   - choosing b2 will prepare all interfaces for 24bits/96kHz but you'll
 310     only be able to use one at the same time
 3123.2.3.2 -  USB implementation details for this device
 314You may safely skip this section if you're not interested in driver 
 317This section describes some internal aspects of the device and summarizes the 
 318data I got by usb-snooping the windows and Linux drivers.
 320The M-Audio Audiophile USB has 7 USB Interfaces:
 321a "USB interface":
 322 * USB Interface nb.0
 323 * USB Interface nb.1
 324   - Audio Control function
 325 * USB Interface nb.2
 326   - Analog Output
 327 * USB Interface nb.3
 328   - Digital Output
 329 * USB Interface nb.4
 330   - Analog Input
 331 * USB Interface nb.5
 332   - Digital Input
 333 * USB Interface nb.6
 334   - MIDI interface compliant with the MIDIMAN quirk 
 336Each interface has 5 altsettings (AltSet 1,2,3,4,5) except:
 337 * Interface 3 (Digital Out) has an extra Alset nb.6 
 338 * Interface 5 (Digital In) does not have Alset nb.3 and 5 
 340Here is a short description of the AltSettings capabilities:
 341 * AltSettings 1 corresponds to
 342  - 24-bit depth, 48.1-96kHz sample mode
 343  - Adaptive playback (Ao and Do), Synch capture (Ai), or Asynch capture (Di)
 344 * AltSettings 2 corresponds to
 345  - 24-bit depth, 8-48kHz sample mode
 346  - Asynch capture and playback  (Ao,Ai,Do,Di)
 347 * AltSettings 3 corresponds to
 348  - 24-bit depth, 8-48kHz sample mode
 349  - Synch capture (Ai) and Adaptive playback (Ao,Do)
 350 * AltSettings 4 corresponds to
 351  - 16-bit depth, 8-48kHz sample mode
 352  - Asynch capture and playback  (Ao,Ai,Do,Di)
 353 * AltSettings 5 corresponds to
 354  - 16-bit depth, 8-48kHz sample mode
 355  - Synch capture (Ai) and Adaptive playback (Ao,Do)
 356 * AltSettings 6 corresponds to
 357  - 16-bit depth, 8-48kHz sample mode
 358  - Synch playback (Do), audio format type III IEC1937_AC-3
 360In order to ensure a correct initialization of the device, the driver 
 361_must_know_ how the device will be used:
 362 * if DTS is chosen, only Interface 2 with AltSet nb.6 must be
 363   registered
 364 * if 96KHz only AltSets nb.1 of each interface must be selected
 365 * if samples are using 24bits/48KHz then AltSet 2 must me used if
 366   Digital input is connected, and only AltSet nb.3 if Digital input
 367   is not connected
 368 * if samples are using 16bits/48KHz then AltSet 4 must me used if
 369   Digital input is connected, and only AltSet nb.5 if Digital input
 370   is not connected
 372When device_setup is given as a parameter to the snd-usb-audio module, the 
 373parse_audio_endpoints function uses a quirk called 
 374"audiophile_skip_setting_quirk" in order to prevent AltSettings not 
 375corresponding to device_setup from being registered in the driver.
 3774 - Audiophile USB and Jack support
 380This section deals with support of the Audiophile USB device in Jack.
 382There are 2 main potential issues when using Jackd with the device:
 383* support for Big-Endian devices in 24-bit modes
 384* support for 4-in / 4-out channels
 3864.1 - Direct support in Jackd
 389Jack supports big endian devices only in recent versions (thanks to
 390Andreas Steinmetz for his first big-endian patch). I can't remember 
 391exactly when this support was released into jackd, let's just say that
 392with jackd version 0.103.0 it's almost ok (just a small bug is affecting 
 39316bits Big-Endian devices, but since you've read carefully the above
 394paragraphs, you're now using kernel >= 2.6.23 and your 16bits devices 
 395are now Little Endians ;-) ).
 397You can run jackd with the following command for playback with Ao and
 398record with Ai:
 399  % jackd -R -dalsa -Phw:1,0 -r48000 -p128 -n2 -D -Chw:1,1
 4014.2 - Using Alsa plughw
 403If you don't have a recent Jackd installed, you can downgrade to using
 404the Alsa "plug" converter.
 406For instance here is one way to run Jack with 2 playback channels on Ao and 2 
 407capture channels from Ai:
 408  % jackd -R -dalsa -dplughw:1 -r48000 -p256 -n2 -D -Cplughw:1,1
 410However you may see the following warning message:
 411"You appear to be using the ALSA software "plug" layer, probably a result of 
 412using the "default" ALSA device. This is less efficient than it could be. 
 413Consider using a hardware device instead rather than using the plug layer."
 4154.3 - Getting 2 input and/or output interfaces in Jack
 418As you can see, starting the Jack server this way will only enable 1 stereo
 419input (Di or Ai) and 1 stereo output (Ao or Do).
 421This is due to the following restrictions:
 422* Jack can only open one capture device and one playback device at a time
 423* The Audiophile USB is seen as 2 (or three) Alsa devices: hw:1,0, hw:1,1
 424  (and optionally hw:1,2)
 426If you want to get Ai+Di and/or Ao+Do support with Jack, you would need to
 427combine the Alsa devices into one logical "complex" device.
 429If you want to give it a try, I recommend reading the information from
 430this page:
 431It is related to another device (ice1712) but can be adapted to suit
 432the Audiophile USB.
 434Enabling multiple Audiophile USB interfaces for Jackd will certainly require:
 435* Making sure your Jackd version has the MMAP_COMPLEX patch (see the ice1712 page)
 436* (maybe) patching the alsa-lib/src/pcm/pcm_multi.c file (see the ice1712 page)
 437* define a multi device (combination of hw:1,0 and hw:1,1) in your .asoundrc
 438  file 
 439* start jackd with this device
 441I had no success in testing this for now, if you have any success with this kind 
 442of setup, please drop me an email.
 443 kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.