 In a previous TechTip, we presented a few techniques that allow Windows users of Skype (a popular Web telephony service) to improve the quality of their audio. As with Windows, the quality of the calls under Linux widely varies. There are the ever present problems with echoes, sound delays, the sound dropping out, and problems like that.
However, Linux users of Skype have a unique set of challenges. While current Linux distributions offer great support for many PC audio devices, that support isn't always perfect. You will need to do some tweaking to your system settings and the settings of your Skype client software to improve the audio quality of your Skype calls. This TechTip offers some advice on how to improve the quality of Skype calls under Linux.
Note: This TechTip focuses on making changes in the K Desktop Environment (KDE), a popular Linux window manager. You should be able to adapt the instructions in this TechTip to the window manager that you use.
 Adjusting the Volume
One of the first things that you can do when trying to improve the audio quality of your Skype calls is to adjust the volume of the sound devices on your computer. In KDE, you can adjust the volume of your audio device using the Kmix application.
Using the sliders in the Kmix window, try lowering or raising the volume of the Speaker, Microphone, and PhoneIn settings. You can tell which is which by holding your mouse pointer over a slider for a couple of seconds. You'll need to work with the settings a bit to find the ones that are right for you.
OSS or ALSA?
OSS (Open Sound System) and ALSA (Advanced Linux Sound Architecture) are software that that Linux uses to communicate with sound cards. OSS is the older of the two, while ALSA is younger and supports more sound cards. Most newer Linux distributions come installed with both OSS and ALSA.
The latest version of the Skype client (1.4.0.99 at the time of writing) supports OSS and ALSA. Older versions of the client only support OSS. If you're having audio trouble, try downloading and installing the latest version of the Skype client for Linux.
From there, you can tell the Skype client which sound system to use by selecting Tools>Options, and then clicking Sound Devices. If you have ALSA and OSS installed on your computer, then you can select one or the other from the Audio system to use dropdown list.
If you still run into audio problems with ALSA, try installing the newest version from your package repository of choice or by downloading it from the ALSA Web site. As of this writing, the latest stable version of ALSA is 1.0.14.
Getting aRts-y
aRts is short for Analogue Real-Time Synthesizer, and it's the KDE sound server that's used for playing and recording audio in KDE. aRts actually works in conjunction with OSS and ALSA and its settings can have an effect on the quality of your audio when using the Skype client.
When you hear an echo or heavy background noise when using the Skype client, you can try to decrease or eliminate the echo by changing the size of the aRts sound buffer (the memory KDE uses to hold sound files before they're sent to your computer's sound system). Select KDE Control Center>Sound and Multimedia>Sound System and then click the Sound I/O tab.
 Move the Audio buffer size slider to the left or right. Again, you'll have to experiment a little to get the right setting.
If you're experiencing delays in the sounds going to or from your computer, click the Enable full duplex operation checkbox. Full duplex means that your computer, and specifically the Skype client, can send data in two directions simultaneous. In many cases, doing this can eliminate the delay.
Other Things That You Can Do
Fiddling with your system and Skype client settings isn't the only way to improve the quality of the audio in your Skype calls. There are a number of other things you can try, the first of which is to use a proper Web telephony headset. Some people try to use a microphone and their PC speakers, or the microphone and speakers built into their laptops, when making calls with Skype. That's not the best thing to so. The sound from the speakers can generate feedback in the form of a painful high-pitched squeal. At the very least, you'll get some echo. You can get a decent headset for under $20 (USD). You can also try using a USB handset that is specifically for use with Skype. Some work well in Linux; others don't.
If you're using Skype with a wireless Internet connection, ensure that the signal from the wireless router is strong and reliable. We've noticed variable quality when trying to make Skype calls with our Linux laptops outside of the home on wireless nodes available at universities, coffee shops, and the like. In many cases, the signal was quite strong. In others, signal was poor, which caused sound drop outs and echoes. After a few minutes, some calls were dropped entirely. We found, though, that laptops and notebooks with built-in wireless cards work better than those with PCMCIA wireless cards.
When making PC-to-PC calls using Skype, try to get the people to whom you're talking to optimize the settings of their Skype clients and system sound. Point Linux users to this TechTip, or get them to visit the Skype online forums.
When you make a change, test it. Call friends who use Skype. If you use SkypeOut, be willing to burn up a few of your SkypeOut credits making a call or two to landlines or mobile phones both here and abroad. And don't forget to use Skype's echo1-2-3 call answer service (described here).
The audio quality of your Skype calls depends on a number of factors. With a bit of simple tweaking, you can noticeably improve the way in which your calls sound. The quality of the sound may never be perfect, but you can eliminate much of the echo and background noise. And that goes a long way.
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