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Based on kernel version 3.13. Page generated on 2014-01-20 22:04 EST.

1		Guide to using M-Audio Audiophile USB with ALSA and Jack	v1.5
2		========================================================
3	
4		    Thibault Le Meur <Thibault.LeMeur@supelec.fr>
5	
6	This document is a guide to using the M-Audio Audiophile USB (tm) device with 
7	ALSA and JACK.
8	
9	History
10	=======
11	* v1.4 - Thibault Le Meur (2007-07-11)
12	 - Added Low Endianness nature of 16bits-modes
13	   found by Hakan Lennestal <Hakan.Lennestal@brfsodrahamn.se>
14	 - Modifying document structure
15	* v1.5 - Thibault Le Meur (2007-07-12)
16	 - Added AC3/DTS passthru info
17	
18	
19	1 - Audiophile USB Specs and correct usage
20	==========================================
21	
22	This part is a reminder of important facts about the functions and limitations 
23	of the device.
24	
25	The 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)
35	
36	The 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.
40	Moreover, the Audiophile USB documentation gives the following Warning:
41	"Please exit any audio application running before switching between bit depths"
42	
43	Due to the USB 1.1 bandwidth limitation, a limited number of interfaces can be 
44	activated 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
52	
53	Important facts about the Digital interface:
54	--------------------------------------------
55	 * The Do port additionally supports surround-encoded AC-3 and DTS passthrough, 
56	though 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 
59	to synchronize the device to an external sample clock
60	   - As a consequence, the Di port must be enable only if an active Digital 
61	source is connected
62	   - Enabling Di when no digital source is connected can result in a 
63	synchronization error (for instance sound played at an odd sample rate)
64	
65	
66	2 - Audiophile USB MIDI support in ALSA
67	=======================================
68	
69	The Audiophile USB MIDI ports will be automatically supported once the
70	following modules have been loaded:
71	 * snd-usb-audio
72	 * snd-seq-midi
73	
74	No additional setting is required.
75	
76	
77	3 - Audiophile USB Audio support in ALSA
78	========================================
79	
80	Audio functions of the Audiophile USB device are handled by the snd-usb-audio 
81	module. This module can work in a default mode (without any device-specific 
82	parameter), or in an "advanced" mode with the device-specific parameter called 
83	"device_setup".
84	
85	3.1 - Default Alsa driver mode
86	------------------------------
87	
88	The default behavior of the snd-usb-audio driver is to list the device 
89	capabilities at startup and activate the required mode when required 
90	by the applications: for instance if the user is recording in a 
91	24bit-depth-mode and immediately after wants to switch to a 16bit-depth mode,
92	the snd-usb-audio module will reconfigure the device on the fly.
93	
94	This approach has the advantage to let the driver automatically switch from sample 
95	rates/depths automatically according to the user's needs. However, those who 
96	are using the device under windows know that this is not how the device is meant to
97	work: under windows applications must be closed before using the m-audio control
98	panel to switch the device working mode. Thus as we'll see in next section, this 
99	Default Alsa driver mode can lead to device misconfigurations.
100	
101	Let's get back to the Default Alsa driver mode for now.  In this case the 
102	Audiophile interfaces are mapped to alsa pcm devices in the following 
103	way (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
107	
108	In this mode, the device uses Big Endian byte-encoding so that 
109	supported audio format are S16_BE for 16-bit depth modes and S24_3BE for 
110	24-bits depth mode.
111	
112	One exception is the hw:1,2 port which was reported to be Little Endian 
113	compliant (supposedly supporting S16_LE) but processes in fact only S16_BE streams.
114	This has been fixed in kernel 2.6.23 and above and now the hw:1,2 interface 
115	is reported to be big endian in this default driver mode.
116	
117	Examples:
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
126	
127	If you're happy with the default Alsa driver mode and don't experience any 
128	issue with this mode, then you can skip the following chapter.
129	
130	3.2 - Advanced module setup
131	---------------------------
132	
133	Due to the hardware constraints described above, the device initialization made 
134	by the Alsa driver in default mode may result in a corrupted state of the 
135	device. For instance, a particularly annoying issue is that the sound captured 
136	from the Ai interface sounds distorted (as if boosted with an excessive high
137	volume gain).
138	
139	For people having this problem, the snd-usb-audio module has a new module 
140	parameter called "device_setup" (this parameter was introduced in kernel
141	release 2.6.17)
142	
143	3.2.1 - Initializing the working mode of the Audiophile USB
144	
145	As far as the Audiophile USB device is concerned, this value let the user 
146	specify:
147	 * the sample depth
148	 * the sample rate
149	 * whether the Di port is used or not 
150	
151	When initialized with "device_setup=0x00", the snd-usb-audio module has
152	the same behaviour as when the parameter is omitted (see paragraph "Default 
153	Alsa driver mode" above)
154	
155	Others modes are described in the following subsections.
156	
157	3.2.1.1 - 16-bit modes
158	
159	The two supported modes are:
160	
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
166	
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
172	
173	In this modes the device operates only at 16bits-modes. Before kernel 2.6.23,
174	the devices where reported to be Big-Endian when in fact they were Little-Endian
175	so 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
177	where "test_S16_LE.raw" was in fact a little-endian sample file.
178	
179	Thanks to Hakan Lennestal (who discovered the Little-Endiannes of the device in
180	these modes) a fix has been committed (expected in kernel 2.6.23) and
181	Alsa now reports Little-Endian interfaces. Thus playing a file now is as simple as
182	using:
183	   % aplay -D hw:1,1 -c2 -t raw -r48000 -fS16_LE test_S16_LE.raw
184	
185	3.2.1.2 - 24-bit modes
186	
187	The three supported modes are:
188	
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
194	
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
201	
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
209	
210	In these modes the device is only Big-Endian compliant (see "Default Alsa driver 
211	mode" above for an aplay command example)
212	
213	3.2.1.3 - AC3 w/ DTS passthru mode
214	
215	Thanks to Hakan Lennestal, I now have a report saying that this mode works.
216	
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
221	
222	The 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
224	
225	3.2.2 - How to use the device_setup parameter
226	----------------------------------------------
227	
228	The parameter can be given:
229	
230	 * By manually probing the device (as root):
231	   # modprobe -r snd-usb-audio
232	   # modprobe snd-usb-audio index=1 device_setup=0x09
233	
234	 * Or while configuring the modules options in your modules configuration file
235	   (typically 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
238	
239	CAUTION when initializing the device
240	-------------------------------------
241	
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.
245	
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.
249	
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.
260	
261	3.2.3 - Technical details for hackers
262	-------------------------------------
263	This section is for hackers, wanting to understand details about the device
264	internals and how Alsa supports it.
265	
266	3.2.3.1 - Audiophile USB's device_setup structure
267	
268	If you want to understand the device_setup magic numbers for the Audiophile 
269	USB, you need some very basic understanding of binary computation. However, 
270	this is not required to use the parameter and you may skip this section.
271	
272	The device_setup is one byte long and its structure is the following:
273	
274	       +---+---+---+---+---+---+---+---+
275	       | b7| b6| b5| b4| b3| b2| b1| b0|
276	       +---+---+---+---+---+---+---+---+
277	       | 0 | 0 | 0 | Di|24B|96K|DTS|SET|
278	       +---+---+---+---+---+---+---+---+
279	
280	Where:
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
303	
304	Caution:
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
311	
312	3.2.3.2 -  USB implementation details for this device
313	
314	You may safely skip this section if you're not interested in driver 
315	hacking.
316	
317	This section describes some internal aspects of the device and summarizes the 
318	data I got by usb-snooping the windows and Linux drivers.
319	
320	The M-Audio Audiophile USB has 7 USB Interfaces:
321	a "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 
335	
336	Each 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 
339	
340	Here 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
359	
360	In 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
371	
372	When device_setup is given as a parameter to the snd-usb-audio module, the 
373	parse_audio_endpoints function uses a quirk called 
374	"audiophile_skip_setting_quirk" in order to prevent AltSettings not 
375	corresponding to device_setup from being registered in the driver.
376	
377	4 - Audiophile USB and Jack support
378	===================================
379	
380	This section deals with support of the Audiophile USB device in Jack.
381	
382	There 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
385	
386	4.1 - Direct support in Jackd
387	-----------------------------
388	
389	Jack supports big endian devices only in recent versions (thanks to
390	Andreas Steinmetz for his first big-endian patch). I can't remember 
391	exactly when this support was released into jackd, let's just say that
392	with jackd version 0.103.0 it's almost ok (just a small bug is affecting 
393	16bits Big-Endian devices, but since you've read carefully the above
394	paragraphs, you're now using kernel >= 2.6.23 and your 16bits devices 
395	are now Little Endians ;-) ).
396	
397	You can run jackd with the following command for playback with Ao and
398	record with Ai:
399	  % jackd -R -dalsa -Phw:1,0 -r48000 -p128 -n2 -D -Chw:1,1
400	
401	4.2 - Using Alsa plughw
402	-----------------------
403	If you don't have a recent Jackd installed, you can downgrade to using
404	the Alsa "plug" converter.
405	
406	For instance here is one way to run Jack with 2 playback channels on Ao and 2 
407	capture channels from Ai:
408	  % jackd -R -dalsa -dplughw:1 -r48000 -p256 -n2 -D -Cplughw:1,1
409	
410	However you may see the following warning message:
411	"You appear to be using the ALSA software "plug" layer, probably a result of 
412	using the "default" ALSA device. This is less efficient than it could be. 
413	Consider using a hardware device instead rather than using the plug layer."
414	
415	4.3 - Getting 2 input and/or output interfaces in Jack
416	------------------------------------------------------
417	
418	As you can see, starting the Jack server this way will only enable 1 stereo
419	input (Di or Ai) and 1 stereo output (Ao or Do).
420	
421	This 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)
425	
426	If you want to get Ai+Di and/or Ao+Do support with Jack, you would need to
427	combine the Alsa devices into one logical "complex" device.
428	
429	If you want to give it a try, I recommend reading the information from
430	this page: http://www.sound-man.co.uk/linuxaudio/ice1712multi.html
431	It is related to another device (ice1712) but can be adapted to suit
432	the Audiophile USB.
433	
434	Enabling 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
440	
441	I had no success in testing this for now, if you have any success with this kind 
442	of setup, please drop me an email.
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