Microsoft KB Archive/943253

= You notice timing jitter and clock drift when you perform an editing operation or a playback operation on a MIDI audio device in Windows Vista =

Article ID: 943253

Article Last Modified on 12/4/2007

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APPLIES TO


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

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SYMPTOMS
On a computer that is running Windows Vista, you perform an editing operation or a playback operation on a MIDI audio device. When you do this, you may notice timing jitter and clock drift.

This problem occurs if the following conditions are true:
 * The MIDI device does not reside on the peripheral component interconnect (PCI) bus.
 * The MIDI device does not advertise any audio endpoints.



CAUSE
This problem occurs because the Dmusic.sys file was removed in Windows Vista. This file is a kernel mode synthesizer of the Microsoft DirectMusic components. This kernel mode synthesizer supplies the DirectMusic components with a high-resolution timer in operating systems that are earlier than Windows Vista.

When the synthesizer was removed, no other kernel mode component supported a DirectMusic clock. Therefore, Windows Vista uses the clock that is provided by the WinMM component.



Hotfix information
A supported hotfix is now available from Microsoft. However, this hotfix is intended to correct only the problem that is described in this article. Apply this hotfix only to systems that are experiencing this specific problem. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next Windows Vista service pack that contains this hotfix.

To resolve this problem, submit a request to Microsoft Online Customer Services to obtain the hotfix. To submit an online request to obtain the hotfix, visit the following Microsoft Web site:

http://go.microsoft.com/?linkid=6294451

Note If additional issues occur or any troubleshooting is required, you might have to create a separate service request. The usual support costs will apply to additional support questions and issues that do not qualify for this specific hotfix. To create a separate service request, visit the following Microsoft Web site:

http://support.microsoft.com/contactus/?ws=support

After you apply this hotfix, Windows Vista uses the QueryPerformanceCounter function from the user mode to provide a high resolution clock.

Prerequisites
There are no prerequisites for installing this hotfix.

Restart requirement
You do not have to restart the computer after you apply this hotfix.

Hotfix replacement information
This hotfix does not replace a previously released hotfix.

Registry information
To use one of the hotfixes in this package, you do not have to make any changes to the registry.

File information
The English version of this hotfix has the file attributes (or later file attributes) that are listed in the following table. The dates and times for these files are listed in Coordinated Universal Time (UTC). When you view the file information, it is converted to local time. To find the difference between UTC and local time, use the Time Zone tab in the Date and Time item in Control Panel.

Windows Vista, x86-based versions


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 software update terminology, click the following article number to view the article in the Microsoft Knowledge Base:

824684 Description of the standard terminology that is used to describe Microsoft software updates

Additional query words: Midi Timing drift jitter

Keywords: kbfix kbqfe kbexpertiseadvanced kbhotfixserver KB943253

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