Troubleshooting In-game Voice Features

http://support.steampowered.com/cgi-bin/steampowered.cfg/php/enduser/std_adp.php?p_faqid=175

If you're having trouble with the voice features, you might see better performance by setting a command line parameter in Steam:

1. In your "Games" list, right-click on the game title.
2. Select "Properties" from the popup menu, and then select "Launch Options" on the dialog that comes up.

Enter "+voice_dsound 0", and then click OK.