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

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.

Back to the top

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.

Back to the top

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: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: 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

File name	File version	File size	Date	Time	Platform
Update.mum	Not applicable	1,775	19-Nov-2007	23:05	Not applicable
X86_5166fccd65d13f0f63837acd69d0c871_31bf3856ad364e35_6.0.6000.20723_none_878b61be7dd8eff5.manifest	Not applicable	700	19-Nov-2007	23:05	Not applicable
X86_microsoft-windows-audio-dmusic_31bf3856ad364e35_6.0.6000.20723_none_4484db1caba7621a.manifest	Not applicable	225,835	19-Nov-2007	23:05	Not applicable
Dmband.dll	6.0.6000.20723	30,208	17-Nov-2007	04:10	x86
Dmcompos.dll	6.0.6000.20723	62,976	17-Nov-2007	04:10	x86
Dmime.dll	6.0.6000.20723	178,688	17-Nov-2007	04:10	x86
Dmloader.dll	6.0.6000.20723	38,400	17-Nov-2007	04:10	x86
Dmscript.dll	6.0.6000.20723	84,480	17-Nov-2007	04:10	x86
Dmstyle.dll	6.0.6000.20723	105,472	17-Nov-2007	04:10	x86
Dmsynth.dll	6.0.6000.20723	105,472	17-Nov-2007	04:10	x86
Dmusic.dll	6.0.6000.20723	101,888	17-Nov-2007	04:10	x86
Dswave.dll	6.0.6000.20723	20,992	17-Nov-2007	04:10	x86

Back to the top

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

Back to the top

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

Back to the top