Configuring Linux for a Bluetooth Stereo Headset BLUE SOUND

COVER STORY Bluetooth Headsets

Configuring Linux for a Bluetooth stereo headset BLUE SOUND

We’ll show you how to set up support for a Bluetooth stereo headset.

BY MARCEL HILZINGER

any Linux users enjoy listening tion, see the Bluetooth ALSA project SCO typically uses mono sound quality. to music through audio players page [2]. The SCO profile lets users send and re- Msuch as XMMS, Amarok, and ceive sound at the same time. In contrast Kaffeine. These players typically output Mono or Stereo to this, the A2DP profile is designed for sound to speakers or headphones at- Bluetooth supports two profiles for high-quality stereo sound. To achieve tached directly to the computer. If you transmitting audio signals: Synchronous this higher quality, A2DP uses a unidi- prefer the headphone option, and if you Connection Oriented (SCO) and Ad- rectional connection with high latency are the kind of listener who needs room vanced Audio Distribution Profile (slow response). to dance, you might want to consider (A2DP). The SCO profile defines a bidi- A Bluetooth headset might support using a wireless Bluetooth headset. rectional connection with fast response only SCO, only A2DP, or both profiles. Low-fidelity wireless headsets for two- (low latency) for voice transmissions. Single-ear headsets of the type common way radios and telephones have been on the market for years, but Bluetooth- based wireless stereo is a more recent phenomenon. Many operating systems do not provide built-in support for Blue- tooth stereo, relying instead on third- party tools. Linux, on the other hand, really does let you directly configure your system to support a Bluetooth stereo headset. This article is based on the excellent HOWTO for Ubuntu [1], although the instructions will work with any distribution that has a recent kernel and a Blue- Figure 1: The Bluetooth headsets by Jabra (left) and Logitech (right) both support stereo tooth stack. For more detailed informa- sound. The Jabra headset also supports the mono SCO profile.

38 ISSUE 80 JULY 2007 WWW.LINUX - MAGAZINE.COM Bluetooth Headsets COVER STORY

The Old Method If the approach that uses the A2DP btsco v0.42 daemon does not work properly, you Device is 1:0 might want to try the old method based on the snd-bt-sco kernel module. This Voice setting: 0x0060 said, I didn’t experience a single case in RFCOMM channel 1 connected which snd-bt-sco worked but the A2DP Using interface hci0 daemon didn’t. Now, pop up a second console and enter To create the snd-bt-sco.ko kernel mod- the following command to start the out- ule, download the CVS code for btsco put: and sbc, build and install as described above, then change directory to btsco/ mpg123 --au - file.mp3 | U kernel and run the make command. Be- a2play Bt-address come root, and copy the module to /lib/ For playback, you need to replace file. modules/Kernelversion/kernel/drivers/ mp3 with the name of any MP3 file and bluetooth. Typing uname -a gives you Bt-address with the Bluetooth address your Kernelversion. for your headset. If you then see the If all of this works, you can load the mod- messages ule by typing modprobe snd-bt-sco. Listen thread running The next step is to associate with the Bluetooth headset. To do so, you need to read 2C00C0 2873 times / sec. make sure the headset is in pairing read 30ABC0 1197 times / sec. mode. Enter the command line: read 3061C0 1198 times / sec. btsco -r -v Bt-address read 2FF0C0 1120 times / sec. Making sure to replace Bt-address with read 3052C0 1154 times / sec. the Bluetooth address for your headset. Herbert Herbert Matern, Fotolia If you see the error message you can be sure that playback is running. The kernel module approach has a cou- btsco v0.42 ple of major disadvantages compared Error: control open (hw:1): U with the A2DP daemon. For example, No such device to play a track, you need to enter commands at the command line – playlists Error: Can't find device. Bail are not supported – and whenever you either your headset is not supported by update the kernel, you will need to install the module, or the kernel module might for mobile telephony typically support a new module. In addition, playback did not be loaded. If everything works out, just the SCO profile, whereas stereo not work at all on the Logitech headset you should see the following message: because it does not support SCO. headsets often support both. In our lab, I tested the BT620s stereo headset by Jabra and the Wireless Headphones for You can refer to the box called “The Old ./bootstrap PC by Logitech (Figure 1). The Jabra de- Method” for instructions on the more ./configure --prefix=/usr vice supports both SCO and A2DP. The complicated setup for a SCO connection. make LED flash sequence tells you which This can be interesting if you would like sudo make install mode the headset is working in. The to use a headset for phoning (via Skype, Logitech headset only supports A2DP. In for example). Depending on your distribution, you will fact, the Logitech headset is not officially For the A2DP daemon, you need the need to enter either the root password a Bluetooth device: Logitech sells it with sbc library and the Bluetooth-ALSA tool (SUSE, Fedora), or your user password a USB dongle as a normal wireless solu- btsco. See the box titled “Downloading (Ubuntu) to install with a sudo com- tion, although the set does have Blue- Code from CVS” for details. mand. When you are done, change di- tooth capabilities. After unpacking or downloading the rectory to plugz and enter the same com- This article will be concentrating on source code, change to the sbc directory mands here, adding the --sysconfdir= stereo output via the a2dpd daemon. and enter the following commands: /etc option to the ./configure command:

Downloading Code from CVS

After logging in, you’re prompted to enter your password. Just press Enter. cvs -d:pserver:[email protected]:/cvsroot/sbc login cvs -d:pserver:[email protected]:/cvsroot/sbc co sbc cvs -d:pserver:[email protected]:/cvsroot/bluetooth-alsa login cvs -d:pserver:[email protected]:/cvsroot/bluetooth-alsa co plugz

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./bootstrap fails to find a Bluetooth device, either will then see the following message in ./configure --prefix=U your computer’s Bluetooth dongle is not the terminal window with the a2dpd /usr --sysconfdir=/etc working or the headset is not in pairing command: make mode. To find out whether Linux has sudo make install detected the dongle, give the hcitool dev DEBUG: a2dp_transfer_raw: U command. It should display the Blue- Bandwith: 27250 (212 kbps) 32 This completes the installation. The next tooth address for the dongle. step is to configure the A2DP daemon. Instead of XMMS, you could just as eas- Let’s Rock ily use Amarok or Kaffeine for sound Configuration Files If you have created the two configura- output. To do so in Amarok, select Set- For playback, you need to tell the dae- tion files for the ALSA configuration and tings | Configure Amarok | Audio output, mon which headset to use, and you need the A2DP daemon, you can launch the and set the Output module to Alsa. After a .asoundrc file to create a matching daemon at the command line by typing clicking on Apply, enter the a2dpd de- ALSA device. If you do not have a a2dpd. You don’t need to be root to do vice in both the Mono and Stereo boxes .asoundrc file in your home directory, this. The following two lines should (Figure 2). create a new file like so: appear as output: In Kaffeine, select Settings | Xine En- gine Parameters | Audio, click the Expert pcm.a2dpd { avrcp: Accepting U Options tab, and scroll down until you type a2dpd incoming connection see device.alsa_front_device device used } avdtp: Accepting U for stereo output. Instead of default, incoming connection enter a2dpd here. If the file already exists, add the three preceding lines at the end of the file. To If you see an error message stating Can- Pros and Cons configure the A2DP daemon, copy the not open /dev/ input/ uinput: No such file One of the biggest advantages of the sample.a2dprc file called .a2dprc from or directory, you can just ignore it. Bluetooth approach compared with leg- the plugz/also-plugins directory to your Leaving the terminal window open, acy wireless headsets is that you can use home directory. Note that both files start launch XMMS and press Ctrl+P to open a Bluetooth headset to send commands with a dot. Then open the .a2dprc file, the configuration dialog. As your Output to your Linux computer. For example, remove the pound sign (#) in line 48 to Plugin, select ALSA [libALSA.so] and you can stop the player, move to the next enable the entry #address=00:08: then click on Configure. In the Audio track, or backtrack. F4:30:07:64, and replace the Bluetooth device box, manually enter a2dpd (you The .a2dprc file specifies which com- address in this entry with the address for can’t select the device from the list), and mands the A2DP daemon receives when your dongle. To find the address, refer to then click OK twice to apply the settings. you press a button. In the # AVRCP Com- the next section. When you start to play back in Bluetooth Basics XMMS, a dialog To play music on your headset, you need box appears, to connect it to your PC. To allow this to prompting you to happen, you need to make sure your pair the device. headset is visible. If you have a Jabra The headset must headset, press the pads on both ear- be in pairing mode phones for about five seconds. You can for this. tell that the headset is in pairing mode On SUSE Linux, because the LEDs will alternately flash the pairing dialog red, blue, and green. appears in the If you have the Logitech headset, hold KDE Bluetooth down the button at the center of the left framework; on earphone until the LED starts to flash Ubuntu, you will quickly. Now enter hcitool scan at the see a Gnome command line, and you should see the Bluetooth dialog Bluetooth address and name of the head- box, assuming sets – for example: you have installed the bluez-passkey- marcel@kim:~> hcitool scan gnome package on Scanning ... Edgy. 00:13:17:70:44:5A Jabra BT620s If pairing works as intended, the Now enter this address in the .a2dprc file player should start Figure 2: To be able to play music via the A2DP daemon, you need to in your home directory. If the command to play back. You set up a2dpd as an ALSA device in Amarok.

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mands to run section, you need to en- though the sound provided by the A2DP player takes about a second to react; ter commands for XMMS. If you prefer profile was far superior to that of the however, this is not a genuine issue. The to use Amarok, replace, for example, SCO connection, which is designed solution is not currently recommended cmdplay=xmms --play with cmdplay= for voice only, some background noise for video playback: With some video, amarok -p, enter amarok --previous for clouded what was otherwise a very I only heard the voices, and the sound- cmdprev=, and so on. In the a2dpd positive impression. track was distorted or nonexistent. window, you will see which commands Some latency issues occurred with the daemon sends. some versions of the daemon. For exam- Conclusions The same file is used to set the trans- ple, the daemon stopped playing back in Now you can enjoy wireless fun with mission bandwidth. By default, a2dpd an early version from November 7, 2006, stereo sound via Bluetooth. It is worth uses a maximum of 256Kbps. If you if the headset was out of range, and then mentioning that Linux is a pioneer in want to increase the bandwidth, change it played the notes it had missed at dou- this field. Mac OS-X Bluetooth versions the value for sbcbitpool from 32 to 64. ble or triple speed once the headset was only support the SCO profile; Apple In our lab, I experienced some dropouts back in range. plans to introduce A2DP sound with its doing so. Assessing the value of 16 After applying a patch by Fréderic Dal- future “Leopard” OS-X release. reduces the maximum bandwidth to leau, who is currently continuing the de- Windows XP is also behind on tools 128Kbps; however, the sound quality velopment of Bluetooth-Alsa in coopera- for playing stereo sound with Bluetooth. is inferior at this bit rate. tion with Brad Migley, this problem dis- Vista needs to resort to a third-party Because the Bluetooth headset auto- appeared. However, the latency prob- vendor for an A2DP profile. ■ matically contacts the A2DP server, you lems occurred in a CVS version from can develop a configuration to transmit November 15. INFO the stream from one computer to an- This time, the speed wowed and flut- [1] Ubuntu Bluetooth Audio HOWTO: other with some tinkering; this might be tered after short periods of dropout dur- https:// help. ubuntu. com/ community/ useful if you want to cover the whole of ing playback. If you remember the days BluetoothAudio a large building, for example. of vinyl, you can probably imagine what [2] Bluetooth ALSA Project homepage: I wasn’t entirely happy with the sound that sounds like. Because of the slow re- http:// bluetooth-alsa. sourceforge. net quality of the Bluetooth solution. Al- sponse of the A2DP connection, the

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