1 ========================================================
2 Guide to using M-Audio Audiophile USB with ALSA and Jack
3 ========================================================
4
5 v1.5
6
7 Thibault Le Meur <Thibault.LeMeur@supelec.fr>
8
9 This document is a guide to using the M-Audio Audiophile USB (tm) device with
10 ALSA and JACK.
11
12 History
13 =======
14
15 * v1.4 - Thibault Le Meur (2007-07-11)
16
17 - Added Low Endianness nature of 16bits-modes
18 found by Hakan Lennestal <Hakan.Lennestal@brfsodrahamn.se>
19 - Modifying document structure
20
21 * v1.5 - Thibault Le Meur (2007-07-12)
22 - Added AC3/DTS passthru info
23
24
25 Audiophile USB Specs and correct usage
26 ======================================
27
28 This part is a reminder of important facts about the functions and limitations
29 of the device.
30
31 The device has 4 audio interfaces, and 2 MIDI ports:
32
33 * Analog Stereo Input (Ai)
34
35 - This port supports 2 pairs of line-level audio inputs (1/4" TS and RCA)
36 - When the 1/4" TS (jack) connectors are connected, the RCA connectors
37 are disabled
38
39 * Analog Stereo Output (Ao)
40 * Digital Stereo Input (Di)
41 * Digital Stereo Output (Do)
42 * Midi In (Mi)
43 * Midi Out (Mo)
44
45 The internal DAC/ADC has the following characteristics:
46
47 * sample depth of 16 or 24 bits
48 * sample rate from 8kHz to 96kHz
49 * Two interfaces can't use different sample depths at the same time.
50
51 Moreover, the Audiophile USB documentation gives the following Warning:
52 Please exit any audio application running before switching between bit depths
53
54 Due to the USB 1.1 bandwidth limitation, a limited number of interfaces can be
55 activated at the same time depending on the audio mode selected:
56
57 * 16-bit/48kHz ==> 4 channels in + 4 channels out
58
59 - Ai+Ao+Di+Do
60
61 * 24-bit/48kHz ==> 4 channels in + 2 channels out,
62 or 2 channels in + 4 channels out
63
64 - Ai+Ao+Do or Ai+Di+Ao or Ai+Di+Do or Di+Ao+Do
65
66 * 24-bit/96kHz ==> 2 channels in _or_ 2 channels out (half duplex only)
67
68 - Ai or Ao or Di or Do
69
70 Important facts about the Digital interface:
71 --------------------------------------------
72
73 * The Do port additionally supports surround-encoded AC-3 and DTS passthrough,
74 though I haven't tested it under Linux
75
76 - Note that in this setup only the Do interface can be enabled
77
78 * Apart from recording an audio digital stream, enabling the Di port is a way
79 to synchronize the device to an external sample clock
80
81 - As a consequence, the Di port must be enable only if an active Digital
82 source is connected
83 - Enabling Di when no digital source is connected can result in a
84 synchronization error (for instance sound played at an odd sample rate)
85
86
87 Audiophile USB MIDI support in ALSA
88 ===================================
89
90 The Audiophile USB MIDI ports will be automatically supported once the
91 following modules have been loaded:
92
93 * snd-usb-audio
94 * snd-seq-midi
95
96 No additional setting is required.
97
98
99 Audiophile USB Audio support in ALSA
100 ====================================
101
102 Audio functions of the Audiophile USB device are handled by the snd-usb-audio
103 module. This module can work in a default mode (without any device-specific
104 parameter), or in an "advanced" mode with the device-specific parameter called
105 ``device_setup``.
106
107 Default Alsa driver mode
108 ------------------------
109
110 The default behavior of the snd-usb-audio driver is to list the device
111 capabilities at startup and activate the required mode when required
112 by the applications: for instance if the user is recording in a
113 24bit-depth-mode and immediately after wants to switch to a 16bit-depth mode,
114 the snd-usb-audio module will reconfigure the device on the fly.
115
116 This approach has the advantage to let the driver automatically switch from sample
117 rates/depths automatically according to the user's needs. However, those who
118 are using the device under windows know that this is not how the device is meant to
119 work: under windows applications must be closed before using the m-audio control
120 panel to switch the device working mode. Thus as we'll see in next section, this
121 Default Alsa driver mode can lead to device misconfigurations.
122
123 Let's get back to the Default Alsa driver mode for now. In this case the
124 Audiophile interfaces are mapped to alsa pcm devices in the following
125 way (I suppose the device's index is 1):
126
127 * hw:1,0 is Ao in playback and Di in capture
128 * hw:1,1 is Do in playback and Ai in capture
129 * hw:1,2 is Do in AC3/DTS passthrough mode
130
131 In this mode, the device uses Big Endian byte-encoding so that
132 supported audio format are S16_BE for 16-bit depth modes and S24_3BE for
133 24-bits depth mode.
134
135 One exception is the hw:1,2 port which was reported to be Little Endian
136 compliant (supposedly supporting S16_LE) but processes in fact only S16_BE streams.
137 This has been fixed in kernel 2.6.23 and above and now the hw:1,2 interface
138 is reported to be big endian in this default driver mode.
139
140 Examples:
141
142 * playing a S24_3BE encoded raw file to the Ao port::
143
144 % aplay -D hw:1,0 -c2 -t raw -r48000 -fS24_3BE test.raw
145
146 * recording a S24_3BE encoded raw file from the Ai port::
147
148 % arecord -D hw:1,1 -c2 -t raw -r48000 -fS24_3BE test.raw
149
150 * playing a S16_BE encoded raw file to the Do port::
151
152 % aplay -D hw:1,1 -c2 -t raw -r48000 -fS16_BE test.raw
153
154 * playing an ac3 sample file to the Do port::
155
156 % aplay -D hw:1,2 --channels=6 ac3_S16_BE_encoded_file.raw
157
158 If you're happy with the default Alsa driver mode and don't experience any
159 issue with this mode, then you can skip the following chapter.
160
161 Advanced module setup
162 ---------------------
163
164 Due to the hardware constraints described above, the device initialization made
165 by the Alsa driver in default mode may result in a corrupted state of the
166 device. For instance, a particularly annoying issue is that the sound captured
167 from the Ai interface sounds distorted (as if boosted with an excessive high
168 volume gain).
169
170 For people having this problem, the snd-usb-audio module has a new module
171 parameter called ``device_setup`` (this parameter was introduced in kernel
172 release 2.6.17)
173
174 Initializing the working mode of the Audiophile USB
175 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
176
177 As far as the Audiophile USB device is concerned, this value let the user
178 specify:
179
180 * the sample depth
181 * the sample rate
182 * whether the Di port is used or not
183
184 When initialized with ``device_setup=0x00``, the snd-usb-audio module has
185 the same behaviour as when the parameter is omitted (see paragraph "Default
186 Alsa driver mode" above)
187
188 Others modes are described in the following subsections.
189
190 16-bit modes
191 ~~~~~~~~~~~~
192
193 The two supported modes are:
194
195 * ``device_setup=0x01``
196
197 - 16bits 48kHz mode with Di disabled
198 - Ai,Ao,Do can be used at the same time
199 - hw:1,0 is not available in capture mode
200 - hw:1,2 is not available
201
202 * ``device_setup=0x11``
203
204 - 16bits 48kHz mode with Di enabled
205 - Ai,Ao,Di,Do can be used at the same time
206 - hw:1,0 is available in capture mode
207 - hw:1,2 is not available
208
209 In this modes the device operates only at 16bits-modes. Before kernel 2.6.23,
210 the devices where reported to be Big-Endian when in fact they were Little-Endian
211 so that playing a file was a matter of using:
212 ::
213
214 % aplay -D hw:1,1 -c2 -t raw -r48000 -fS16_BE test_S16_LE.raw
215
216 where "test_S16_LE.raw" was in fact a little-endian sample file.
217
218 Thanks to Hakan Lennestal (who discovered the Little-Endiannes of the device in
219 these modes) a fix has been committed (expected in kernel 2.6.23) and
220 Alsa now reports Little-Endian interfaces. Thus playing a file now is as simple as
221 using:
222 ::
223
224 % aplay -D hw:1,1 -c2 -t raw -r48000 -fS16_LE test_S16_LE.raw
225
226
227 24-bit modes
228 ~~~~~~~~~~~~
229
230 The three supported modes are:
231
232 * ``device_setup=0x09``
233
234 - 24bits 48kHz mode with Di disabled
235 - Ai,Ao,Do can be used at the same time
236 - hw:1,0 is not available in capture mode
237 - hw:1,2 is not available
238
239 * ``device_setup=0x19``
240
241 - 24bits 48kHz mode with Di enabled
242 - 3 ports from {Ai,Ao,Di,Do} can be used at the same time
243 - hw:1,0 is available in capture mode and an active digital source must be
244 connected to Di
245 - hw:1,2 is not available
246
247 * ``device_setup=0x0D`` or ``0x10``
248
249 - 24bits 96kHz mode
250 - Di is enabled by default for this mode but does not need to be connected
251 to an active source
252 - Only 1 port from {Ai,Ao,Di,Do} can be used at the same time
253 - hw:1,0 is available in captured mode
254 - hw:1,2 is not available
255
256 In these modes the device is only Big-Endian compliant (see "Default Alsa driver
257 mode" above for an aplay command example)
258
259 AC3 w/ DTS passthru mode
260 ~~~~~~~~~~~~~~~~~~~~~~~~
261
262 Thanks to Hakan Lennestal, I now have a report saying that this mode works.
263
264 * ``device_setup=0x03``
265
266 - 16bits 48kHz mode with only the Do port enabled
267 - AC3 with DTS passthru
268 - Caution with this setup the Do port is mapped to the pcm device hw:1,0
269
270 The command line used to playback the AC3/DTS encoded .wav-files in this mode:
271 ::
272
273 % aplay -D hw:1,0 --channels=6 ac3_S16_LE_encoded_file.raw
274
275 How to use the ``device_setup`` parameter
276 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
277
278 The parameter can be given:
279
280 * By manually probing the device (as root):::
281
282 # modprobe -r snd-usb-audio
283 # modprobe snd-usb-audio index=1 device_setup=0x09
284
285 * Or while configuring the modules options in your modules configuration file
286 (typically a .conf file in /etc/modprobe.d/ directory:::
287
288 alias snd-card-1 snd-usb-audio
289 options snd-usb-audio index=1 device_setup=0x09
290
291 CAUTION when initializing the device
292 -------------------------------------
293
294 * Correct initialization on the device requires that device_setup is given to
295 the module BEFORE the device is turned on. So, if you use the "manual probing"
296 method described above, take care to power-on the device AFTER this initialization.
297
298 * Failing to respect this will lead to a misconfiguration of the device. In this case
299 turn off the device, unprobe the snd-usb-audio module, then probe it again with
300 correct device_setup parameter and then (and only then) turn on the device again.
301
302 * If you've correctly initialized the device in a valid mode and then want to switch
303 to another mode (possibly with another sample-depth), please use also the following
304 procedure:
305
306 - first turn off the device
307 - de-register the snd-usb-audio module (modprobe -r)
308 - change the device_setup parameter by changing the device_setup
309 option in ``/etc/modprobe.d/*.conf``
310 - turn on the device
311
312 * A workaround for this last issue has been applied to kernel 2.6.23, but it may not
313 be enough to ensure the 'stability' of the device initialization.
314
315 Technical details for hackers
316 -----------------------------
317
318 This section is for hackers, wanting to understand details about the device
319 internals and how Alsa supports it.
320
321 Audiophile USB's ``device_setup`` structure
322 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
323
324 If you want to understand the device_setup magic numbers for the Audiophile
325 USB, you need some very basic understanding of binary computation. However,
326 this is not required to use the parameter and you may skip this section.
327
328 The device_setup is one byte long and its structure is the following:
329 ::
330
331 +---+---+---+---+---+---+---+---+
332 | b7| b6| b5| b4| b3| b2| b1| b0|
333 +---+---+---+---+---+---+---+---+
334 | 0 | 0 | 0 | Di|24B|96K|DTS|SET|
335 +---+---+---+---+---+---+---+---+
336
337 Where:
338
339 * b0 is the ``SET`` bit
340
341 - it MUST be set if device_setup is initialized
342
343 * b1 is the ``DTS`` bit
344
345 - it is set only for Digital output with DTS/AC3
346 - this setup is not tested
347
348 * b2 is the Rate selection flag
349
350 - When set to ``1`` the rate range is 48.1-96kHz
351 - Otherwise the sample rate range is 8-48kHz
352
353 * b3 is the bit depth selection flag
354
355 - When set to ``1`` samples are 24bits long
356 - Otherwise they are 16bits long
357 - Note that b2 implies b3 as the 96kHz mode is only supported for 24 bits
358 samples
359
360 * b4 is the Digital input flag
361
362 - When set to ``1`` the device assumes that an active digital source is
363 connected
364 - You shouldn't enable Di if no source is seen on the port (this leads to
365 synchronization issues)
366 - b4 is implied by b2 (since only one port is enabled at a time no synch
367 error can occur)
368
369 * b5 to b7 are reserved for future uses, and must be set to ``0``
370
371 - might become Ao, Do, Ai, for b7, b6, b4 respectively
372
373 Caution:
374
375 * there is no check on the value you will give to device_setup
376
377 - for instance choosing 0x05 (16bits 96kHz) will fail back to 0x09 since
378 b2 implies b3. But _there_will_be_no_warning_ in /var/log/messages
379
380 * Hardware constraints due to the USB bus limitation aren't checked
381
382 - choosing b2 will prepare all interfaces for 24bits/96kHz but you'll
383 only be able to use one at the same time
384
385 USB implementation details for this device
386 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
387
388 You may safely skip this section if you're not interested in driver
389 hacking.
390
391 This section describes some internal aspects of the device and summarizes the
392 data I got by usb-snooping the windows and Linux drivers.
393
394 The M-Audio Audiophile USB has 7 USB Interfaces:
395 a "USB interface":
396
397 * USB Interface nb.0
398 * USB Interface nb.1
399
400 - Audio Control function
401
402 * USB Interface nb.2
403
404 - Analog Output
405
406 * USB Interface nb.3
407
408 - Digital Output
409
410 * USB Interface nb.4
411
412 - Analog Input
413
414 * USB Interface nb.5
415
416 - Digital Input
417
418 * USB Interface nb.6
419
420 - MIDI interface compliant with the MIDIMAN quirk
421
422 Each interface has 5 altsettings (AltSet 1,2,3,4,5) except:
423
424 * Interface 3 (Digital Out) has an extra Alset nb.6
425 * Interface 5 (Digital In) does not have Alset nb.3 and 5
426
427 Here is a short description of the AltSettings capabilities:
428
429 * AltSettings 1 corresponds to
430
431 - 24-bit depth, 48.1-96kHz sample mode
432 - Adaptive playback (Ao and Do), Synch capture (Ai), or Asynch capture (Di)
433
434 * AltSettings 2 corresponds to
435
436 - 24-bit depth, 8-48kHz sample mode
437 - Asynch capture and playback (Ao,Ai,Do,Di)
438
439 * AltSettings 3 corresponds to
440
441 - 24-bit depth, 8-48kHz sample mode
442 - Synch capture (Ai) and Adaptive playback (Ao,Do)
443
444 * AltSettings 4 corresponds to
445
446 - 16-bit depth, 8-48kHz sample mode
447 - Asynch capture and playback (Ao,Ai,Do,Di)
448
449 * AltSettings 5 corresponds to
450
451 - 16-bit depth, 8-48kHz sample mode
452 - Synch capture (Ai) and Adaptive playback (Ao,Do)
453
454 * AltSettings 6 corresponds to
455
456 - 16-bit depth, 8-48kHz sample mode
457 - Synch playback (Do), audio format type III IEC1937_AC-3
458
459 In order to ensure a correct initialization of the device, the driver
460 *must* *know* how the device will be used:
461
462 * if DTS is chosen, only Interface 2 with AltSet nb.6 must be
463 registered
464 * if 96KHz only AltSets nb.1 of each interface must be selected
465 * if samples are using 24bits/48KHz then AltSet 2 must me used if
466 Digital input is connected, and only AltSet nb.3 if Digital input
467 is not connected
468 * if samples are using 16bits/48KHz then AltSet 4 must me used if
469 Digital input is connected, and only AltSet nb.5 if Digital input
470 is not connected
471
472 When device_setup is given as a parameter to the snd-usb-audio module, the
473 parse_audio_endpoints function uses a quirk called
474 ``audiophile_skip_setting_quirk`` in order to prevent AltSettings not
475 corresponding to device_setup from being registered in the driver.
476
477 Audiophile USB and Jack support
478 ===============================
479
480 This section deals with support of the Audiophile USB device in Jack.
481
482 There are 2 main potential issues when using Jackd with the device:
483
484 * support for Big-Endian devices in 24-bit modes
485 * support for 4-in / 4-out channels
486
487 Direct support in Jackd
488 -----------------------
489
490 Jack supports big endian devices only in recent versions (thanks to
491 Andreas Steinmetz for his first big-endian patch). I can't remember
492 exactly when this support was released into jackd, let's just say that
493 with jackd version 0.103.0 it's almost ok (just a small bug is affecting
494 16bits Big-Endian devices, but since you've read carefully the above
495 paragraphs, you're now using kernel >= 2.6.23 and your 16bits devices
496 are now Little Endians ;-) ).
497
498 You can run jackd with the following command for playback with Ao and
499 record with Ai:
500 ::
501
502 % jackd -R -dalsa -Phw:1,0 -r48000 -p128 -n2 -D -Chw:1,1
503
504 Using Alsa plughw
505 -----------------
506
507 If you don't have a recent Jackd installed, you can downgrade to using
508 the Alsa ``plug`` converter.
509
510 For instance here is one way to run Jack with 2 playback channels on Ao and 2
511 capture channels from Ai:
512 ::
513
514 % jackd -R -dalsa -dplughw:1 -r48000 -p256 -n2 -D -Cplughw:1,1
515
516 However you may see the following warning message:
517 You appear to be using the ALSA software "plug" layer, probably a result of
518 using the "default" ALSA device. This is less efficient than it could be.
519 Consider using a hardware device instead rather than using the plug layer.
520
521 Getting 2 input and/or output interfaces in Jack
522 ------------------------------------------------
523
524 As you can see, starting the Jack server this way will only enable 1 stereo
525 input (Di or Ai) and 1 stereo output (Ao or Do).
526
527 This is due to the following restrictions:
528
529 * Jack can only open one capture device and one playback device at a time
530 * The Audiophile USB is seen as 2 (or three) Alsa devices: hw:1,0, hw:1,1
531 (and optionally hw:1,2)
532
533 If you want to get Ai+Di and/or Ao+Do support with Jack, you would need to
534 combine the Alsa devices into one logical "complex" device.
535
536 If you want to give it a try, I recommend reading the information from
537 this page: http://www.sound-man.co.uk/linuxaudio/ice1712multi.html
538 It is related to another device (ice1712) but can be adapted to suit
539 the Audiophile USB.
540
541 Enabling multiple Audiophile USB interfaces for Jackd will certainly require:
542
543 * Making sure your Jackd version has the MMAP_COMPLEX patch (see the ice1712 page)
544 * (maybe) patching the alsa-lib/src/pcm/pcm_multi.c file (see the ice1712 page)
545 * define a multi device (combination of hw:1,0 and hw:1,1) in your .asoundrc
546 file
547 * start jackd with this device
548
549 I had no success in testing this for now, if you have any success with this kind
550 of setup, please drop me an email.
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