Linux SDR – Setting Up a Sound Server
For a few reasons, rather than program the sound card directly I’ve decided to work with JACK (the Jack Audio Connection Kit). First, it provides a well defined interface and framework that hides the complexity of working directly with the sound card. Second, there is a lot of software out there written to interface with JACK that will be useful for DSP work. Finally, it runs on Windows and Mac OSX, which makes it possible to take the work done here and move it to a different platform.
The easiest way to work with JACK is to use the QT Jack Control Interface. To install it on EeeBuntu, select Applications : Add/Remove. From the Add/Remove Applications window, select Sound and Video. Scroll down to the JACK Control entry and check the box, then click Apply Changes.
To start the server, select Applications : Sound & Video : JACK Control.
Click on the Setup button to configure the control. Uncheck the Realtime parameter and set the Input and Output devices to the proper hardware interface. The proper interface can be identified by executing the command
and reading the card number.
To start the server, click the Start button. If everything is ok it will start without error. If it does not, look in the Messages window to see why.
In my case, the server would not start because it did not recognize the USB audio card. This was confusing since card was plugged in and the aplay command showed it listed. However, after a while, I noticed it was listed as only a USB audio device. When I unplugged and replugged the USB cord it came up as Transit USB and the server started with no problem.