An audio device outputs PCM audio instead of DTS audio from the S/PDIF connection or the HDMI connection in Windows Vista

When you click to select the DTS Audio check box in the SPDIF Out Properties dialog box or in the HDMI Out Properties dialog box for an audio device in Windows Vista, the device may output PCM (pulse-code modulation) audio instead of DTS (Digital Theatre System) audio from the Sony/Philips Digital Interface Format (S/PDIF) connection or the High-Definition Multimedia Interface (HDMI) connection. Therefore, you may hear a stereo signal instead of a signal that uses additional channels. Or, you may hear no sound at all. When you click to select the DTS Audio check box, you expect to hear 5.1-channel audio output or another DTS signal.

Note The symptoms of this problem may vary, depending on the specific configuration. For example, any of the following may affect this scenario:

• In most cases, DTS is used to store 5.1-channel audio. However, DTS also supports 2-channel stereo.
• A program that plays DVDs, such as Windows Media Center, may only output DTS audio when it is configured to do this. This behavior may affect what you hear. For example, you may hear no audio from the DVD when this problem occurs.
• Windows Vista tries to use PCM audio for error dialog box notifications. Therefore, you may hear these notifications on a home theater system when this problem occurs.
• When the Dolby Digital check box is selected, you cannot hear sound through AC3-compliant and non-DTS-compliant High-Definition Multimedia Interface (HDMI) devices.

This problem occurs because the DirectShow component and the MPEG2 audio decoder in Windows Vista do not correctly support DTS pass-through over S/PDIF or HDMI.

To work around this problem, click to select both the DTS Audio check box and the Dolby Digital check box in the SPDIF Out Properties dialog box or in the HDMI Out Properties dialog box.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

For more information about audio playback behavior in Windows Vista, click the following article number to view the article in the Microsoft Knowledge Base: