Using the Boston Acoustics Digital BA735 audio system with Linux

So you purchased a really cool set of digital speakers to go with your new system. Great. When you read the documentation that comes with these speakers, you find out you need to plug these into an audio card that supports digital audio.

Such was the case when I got my Gateway machine. I was used to using analog speakers, which work with any audio card, including the Sound Blaster Live! Value Edition that came with the system.

The system came with Boston Digital BA735 speakers. This is a Stereo 2.1 audio system that accepts only digital output.

For those of you who are not familiar with current trends in home entertainment, Stereo 2.1 means that there are two speakers and one subwoofer for enhanced bass and treble, usually needed for better quality output of digital audio, CD playback and DVD playback. Usually the subwoofer is placed on the floor under the desk and the speakers placed on the desk.

Other speaker arrangements in use today are the Stereo 2.0, which is the traditional stereo speaker arrangement, and Stereo 4.1, 5.1 and 7.1. The 4.1, 5.1 and 7.1 refers to the number of speakers used in the arrangement and one subwoofer usually facing the same direction as your PC or TV.

In a 4.1 arrangement, there are two front end speakers and two back end speakers, usually arranged in a rectangle where each speaker is placed in a corner of the rectangle.

The 5.1 arrangement adds a rear center speaker, and the 7.1 adds two speakers on the sides.

On the media side of the home theater system. Stereo audio has two channels. 4.1 requires five audio channels, one for each speaker and one for the subwoofer. Likewise, 5.1 requires six audio channels, and 7.1 requires eight audio channels.

Be sure your audio card supports digital audio

This page covers the Boston Digital BA735 speakers, but much of what is presented here could apply to other digital speakers.

Since the BA735 is a digital audio speaker system, then obviously you need to plug it in to an audio card that supports digital audio. My Gateway machine has the Sound Blaster Live! Value Edition audio card.

Since this is a Sound Blaster card, it is supported by Linux through the emu10k1 driver, which is part of the ALSA subsystem. Newer Sound Blaster cards, namely the Xtreme series, are supported through a commercial Linux driver developed at Creative Labs.

Check the ALSA Project website to see if your audio card is supported, and if digital audio is supported.

Plug your speakers into the Green Jack

Most new digital audio cards have color coded jacks that tell you how to connect your audio devices.

Of interest here is the green jack. This is the analog/digital audio jack that works with any audio system, and is what we use to plug in the BA735 speakers.

The black jack is for rear speakers and is analog only. This is for home theater systems that support analog output.

Activate the digital audio output

When you configure your audio card, the emu10k1 driver is initially configured for analog audio to ensure that the audio card will function properly no matter what is plugged into the green jack.

When analog audio is enabled, the BA735 speakers will not function. You will need to toggle the Digital/Analog Jack for digital output to be enabled.

Make sure the Digital/Analog Jack is set for digital audio output.

Once this has been done, you are now able to use your BA735 speakers. Be sure to adjust the treble and bass settings accordingly. The bass setting is on the subwoofer, and the treble control is on the left speaker.

Do not adjust the bass or treble settings too high, or digital audio will pop in and out, or worse, audio will pop out and you will not be able to hear much from the speakers. If this happens, unplug the speakers, then replug them in to reset the system.

Adjust some volume controls for your environment

On the Boston Digital BA735 speakers, you use the hardware control on the left speaker to adjust the volume.

There are some software controls that also effect the volume of the digital output as well as audio input for recording purposes.

The AC97 Capture is important for recording from Line Input (the blue jack on your audio card). Use the AC97 playback control to monitor input, then set the AC97 Capture likewise before you begin recording.

The AC97 playback control is the software volume control for the speakers.

Configure your audio software for digital input and output

Audio Editing and Recording

You will need to use a audio editing and/or recording package that supports ALSA. I recommend Audacity for this purpose as it is the best of the audio editing software available.

CD Players

The CD players that come with GNOME (gnome-cd) will not work with digital speakers. These are analog only CD player utilities. However, the CD player (kscd) for KDE can be configured for digital audio only on versions 3.5.3 and later of KDE. (SimplyMEPIS is one of those supported distributions where you can configure the CD player to play digital audio.

In kscd, click on Extras, and select Configure KSCD, then with either no audio CD in the drive, or the CD stopped, you can tell KSCD to use digital media extraction to play CDs as digital media rather than conventional CDs. (Actually, this works with any speaker system. Audio CDs contain one audio file for each track on the CD. This file is in CD Audio format, and is the same as a standard WAVE file format, but padded to fit the sectors on a CD, and usually contains a two second gap, i.e. silence between tracks.)

You should instead use a CD ripper or an audio player that supports CD input.

Warning: Thanks to the people at Sony Entertainment, some audio CDs contain rootkits, which compromise the security on your PC. CDs on Sony affiliated recording labels manufactured after 1998 contain these rootkits. When played as a conventional CD, nothing unusual happens. However, when digitally extracted as shown on this page, the rootkit is installed. This was intended to "discourage" copying of audio CDs. This is particularly funny as the same company also sells blank CDs in retail stores.

Audio Players

Audio players such as amaroK, Banshee and XMMS support digital audio. The volume controls on these players also work with digital audio, and hence provide additional volume controls to the BA735 speakers.

To play audio CDs on XMMS, right click on the player window (not the playlist or equalizer), then select Options -> Preferences, click on the Audio I/O Plugins tab, then click on CD Audio Player. Next, click the Configure button.

Select Digital Audio Extraction and click on OK to configure the CD audio plugin to read CD audio tracks from the CD rather than just playing the audio CD.

Then from the Output Plugin menu, select ALSA, then click on OK to configure XMMS for output through the ALSA driver.