M-Audio Transit USB soundcard and Linux

This is a reasonably nice and cheap 24 bit soundcard. It will go up to 96000Hz on play or record (but not both togetehr) and up to 48000 Hz for duplex mode. It has internal support for 24 bit and 16 bit audio. The specs of the card are essentially identical at 24 bit and 16 bit, so there seems no advantage in operating in 24 bit mode (see end of this page) However, Linux and this card do not exist together very well.
It only has a line input, which has a sensitivity of .7V peak to peak for full scale recording (ie anything greater than .7 V will clip if the recording level is set to maximum. If the recording level lower, it will take a higher level input to clip. I do not know what the maximum input level is. It seems to have a 10K ohm input impedance but I am not sure of this.

This card needs to have firmware downloaded to the card on the USB bus to work. It uses a non-standard "DFU" method which seems to have some problems with Linux. It also mixes its Type I and Type III endpoints to confuse the software. I have found (with the help of and software written by Clement Ladisch and Takashi Iwai.) a way to make this card useable.

Firmware

The card requires firmware to be downloaded to the card first for it to work as a soundcard. While it appears on the usb bus with Vendor/ProductID of 0763/2806 this is a very primative usb device that does nothing except wait for firmware.

Get the file ma006100.bin from the Windows driver installation zip file. You can run the Windows installation file in wine on Linux and it will unpack that file. One of the unpacked files is a file called (on mine) Ma006100.BIN. Copy that file somewhere and rename it as ma006100.bin
Alterntively if you have windows running, get the file from Windows/system32/drivers/ directory.
Get the file from the sourceforge project
http://usb-midi-fw.sourceforge.net/ and untar it (tar -xzf madfu-firmware-0.9.tar.gz)
Copy the file ma006100.bin to the directory madfu-firmware-0.9

Kernel Version

For kernels ealier than 2.6.8.1 the usb bus reset code had a severe bug, in that the reset used in the madfuload would make the system completely unstable and lead to an eventual kernel crash. This seems to have been fixed in the later kernels. For later kernels, you should just be able to use Laditsh's script to install the programs (make install) and hotplugging should work.

For ealier Kernels

Edit the file madfuload.c and comment out the lines

		   if (usb_reset() == -1)
		         fatal("cannot reset device - %s", strerror(errno));
	           close(device);

Change them to

		/*
		  if (usb_reset() == -1)
		       fatal("cannot reset device - %s", strerror(errno));
	         close(device);
		 */

Now compile this program.

		       ./configure
		       make

Edit maudio_dfu. This is teh hotplug script which the usb hotplug process runs when it finds the transit plugged into the usb bus.
Change the FIRMWAREDIR to whereever you plan to place the ma006100.bin file.
Change the LOADER to whereever you want to put the loader file madfuloader.
At the end of the file place the lines.
```
	       $LOGGER -t $0 "Resetting the USB bus"
	       /usr/bin/at now + 1 minutes << EOF
	       service usb restart
	       sleep 10
	       alsactl restore
	       EOF
       
```
In Mandrake 9.1, edit the file /etc/init.d/usb and remove the # mark in front of the usb_stop line
```
	       stop)
	       #  usb_stop
               rm -f /var/lock/subsys/usb
	       ;;
       
```
```
	       stop)
	         usb_stop
	          rm -f /var/lock/subsys/usb
	       ;;
       
```
Note that you must make sure that when you issue a
service usb stop
it actually removes the usbcore module. (In the script shipped with Mandrake this did nothing.)
Explanation-- the usb-reset() in madfuloader will, if left in, crash the system making it very unstable and unuseable. This is be due to some bug in the USB subsytem on Linuxi for kernels before 2.6.8.
However, the Linux USB system will not recognise the card, which now is a new card with the firmware loaded without bringing down the usb bus.
However in the hotplug script, when the usb bus comes down, the hotplug program is killed at the same time. This means that if you try to directly run "service usb restart" from the hotplug script it will die when usbcore is removed, and the script will never finish to bring it up again. This is why this program is run from an "at" script which will not die when the usb bus dies.
You must now copy the hotplug script maudio_dfu into /etc/hotplug/usb. You must also get the contents of the file maudio.usermap into the file /etc/hotplug/usb.usermap or into the file /etc/hotplug/usb.usermap.local. For the former, you can either copy it in by hand, or you can copy the maudio.usermap to /usr/lib/hotplug/madfu/usb.usermap and then run update-usb.usermap

Your system should now be able to use the audio card. Plug it into the usb bus. It will take about one minute befor, when you run lsusb you will see 0763:2006 M-Audio Transit as one of the items.

Note that I have no idea what bringing down and then up again the usb bus will do to the other usb items attached to the usb bus. the file

Alsa

I have only run this using Alsa 1.0.1 and the suggestions below will be limited to that case.

Get the alsa-drivers tar file and untar it and go into the top of that directory tree.
Edit the file ./alsa-kernel/usb/usbaudio.c Change the lines

              if (fmt[3] == USB_FORMAT_TYPE_III) {
	       /* FIXME: the format type is really
                * IECxxx
                *        but we give normal PCM
                *        format to get the
	        *        existing
                *        apps working...
                */
                 pcm_format = SNDRV_PCM_FORMAT_S16_LE;

              if (fmt[3] == USB_FORMAT_TYPE_III) {
	       /* FIXME: the format type is really
                * IECxxx
                *        but we give normal PCM
                *        format to get the
	        *        existing
                *        apps working...
                */
		pcm_format = SNDRV_PCM_FORMAT_FLOAT64_BE;

Note that this format cannot handle the FLOAT64, and if any program asks the soundcard to handle it, it will claim it can. It would be nice if there were an "UNKNOWN" format I could use. However leaving the program as it was completely confuses the 16 bit handling of the driver. It will try to use this Type III format, but cannot, and that means that 16 bit audio does not work.

NOw compile and install alsa following the usual instructions. You will either have to reboot or do depmod to get the module dependencies. snd-usb-audio should load, and you should now have a working M-Audio Transit sound card.

Problems

There are still problems.

The taking down and bringing back up of the usb bus would be expected to wreak havoc with any other devices attached to the usb ports on the system. for example if you were printing on a usb printer when the bs came down you might mess up the print job.
The mixer controls are non-standard. While the alsamixer works, neither aumix not kmix work properly. There are only two mixer controls-- playback volume and microphone volume. (together with muting )The playback slider works, but the microphone slider does ot work. It stays pegged at 100% (even if alsamixer says the mocrophone is not at 100%)

Later Kernels and udev

Mandrake/Mandriva since about 10.0 have used udev and hotplug is deprecated. I have now installed the loader into the Mandriva 2006 system.

Get the latest madfuloader -- currently (Feb 06) at 1.0.9 from SourcForge usb-midi-fw project and follow the instructions above re comilation. There is no need to edit any of the files.

Copy the file maudio_dfu into /etc/udev/agents.d/usb/ directory and make it read/execute for everyone.
Now edit the file /etc/udev/rules.d/70-hotplug_map.rules and add the two lines to the end of that file

SUBSYSTEM=="usb",SYSFS{idProduct}=="2806",SYSFS{idVendor}=="0763",RUN+="/etc/udev/agents.d/usb/maudio_dfu"
SUBSYSTEM=="usb",SYSFS{idProduct}=="2006",SYSFS{idVendor}=="0763",RUN+="/sbin/modprobe snd_usb_audio"

Then restart the udev subsystem

service udev restart

The first line will load the firmware onto the card, changing its product id from 2806 to 2006. This will trigger the second line which will load the snd_usb_audio module, which will create the various alsa sound devices in /dev/sound, and if you have the snd_pcm_oss module loaded, the /dev/dsp and /dev/mixer devices.

Transit Performance.

This card is not too bad as a 16 bit card. Using the testing routine xsndtest I get the following results. The card's performance is essentially independent of the playback volume as set in alsamixer. This is good as it indicates very low playback distortion-- all the noise seems to be noise perhaps in the recording circuit. For recording however the card works best with the recording slider about half way up in the alsamixer. Any more or less and the noise figures rise (by less than a dB).

This is a test with the full spectrum pink noise. This is a much more stringent test than the usual harmonic and IM distortion, and it mimics the spectrum of a real music much more accurately. Note that the response is very flat with plus or minus about .05dB from 16Hz to 16KHz. There is a slight imbalance of about 0.1dB between the two channels-- a completely inaudible amount.

These responses were all measured with the output being fed back into the input, so it is difficult to disentagle the output from the input performance.

The noise level, except at the lowest frequencies below about 50Hz is at the one bit level for a 16 bit encoding.(ie the distortion and noise correspond to a level where on average the lowest bit of the output is distortion and noise) Note that the digitisation noise for this signal is about another 10dB lower all across teh spectrum for the 16 bit encoding.

16 bit response

The 24 bit response (feeding the 24 bit pink noise signal out and recording it using aplay in the -D hw:1 mode, and where the 24 bit signal is genuine 24 bits with the digitisation noise now down by another 35dB, and arecord ) is essentially identical to the 16 bit signal. There is no advantage to using this card in the 24 bit mode. It is a very good 16 bit card. It is not a great 24 bit card. (Mind you this is the only 24 bit card I have tested so I do not know if others do better)