Microsoft KB Archive/940685

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

Article ID: 940685

Article Last Modified on 11/26/2007

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APPLIES TO


 * Windows Vista Home Basic 64-bit Edition
 * Windows Vista Home Premium 64-bit Edition
 * Windows Vista Business 64-bit Edition
 * Windows Vista Enterprise 64-bit Edition
 * Windows Vista Ultimate 64-bit Edition
 * Windows Vista Starter
 * Windows Vista Home Basic
 * Windows Vista Home Premium
 * Windows Vista Business
 * Windows Vista Enterprise
 * Windows Vista Ultimate

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SYMPTOMS
When you select the DTS Audio option in the SPDIF 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. 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 select the DTS Audio option, 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.



CAUSE
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.



WORKAROUND
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.



STATUS
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the &quot;Applies to&quot; section.



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

925901 Changes to the audio stack and changes in Windows Media Player audio playback behavior in Windows Vista

Keywords: kbtshoot kbbug kbnofix kbprb kbexpertiseinter KB940685

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