The CPU usage of a high-speed USB 2.0 audio device that is connected to a computer that is running Windows Server 2008 or Windows Vista is greater than the CPU usage of the same device when the device is connected to a Windows XP-based computer

You connect a high-speed USB 2.0 audio device to a computer that is running Windows Server 2008 or Windows Vista. When you operate the USB audio device, you notice that the CPU usage is greater than the CPU usage of the same device when the device is connected to a Windows XP-based computer. You also notice that the CPU usage is greater than the CPU usage of a similar USB audio device that connects as a full-speed USB device. Additionally, you may experience skipping in audio playback from the high-speed USB 2.0 audio device.

Note The increase in the CPU usage may be especially high in a low-performance system.

This problem occurs because of a design change in the USB audio driver (Usbaudio.sys) for Windows Server 2008 and for Windows Vista.

Hotfix information

A supported hotfix is 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 the problem described in this article. This hotfix might receive additional testing. Therefore, if you are not severely affected by this problem, we recommend that you wait for the next software update that contains this hotfix.

If the hotfix is available for download, there is a "Hotfix download available" section at the top of this Knowledge Base article. If this section does not appear, contact Microsoft Customer Service and Support to obtain the hotfix.

Note If additional issues occur or if 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. For a complete list of Microsoft Customer Service and Support telephone numbers or to create a separate service request, visit the following Microsoft Web site: Note The "Hotfix download available" form displays the languages for which the hotfix is available. If you do not see your language, it is because a hotfix is not available for that language.

Important Windows Vista and Windows Server 2008 hotfixes are included in the same packages. However, only one of these products may be listed on the �Hotfix Request� page. To request the hotfix package that applies to both Windows Vista and Windows Server 2008, just select the product that is listed on the page.

Prerequisites

No prerequisites are required for Windows Server 2008-based computers.

To apply this hotfix on Windows Vista-based computers, you must have Windows Vista Service Pack 1 (SP1) installed. For more information about Windows Vista service packs, click the following article number to view the article in the Microsoft Knowledge Base:

Restart requirement

You must restart the computer after you apply this hotfix.

Hotfix replacement information

This hotfix replaces the following hotfixes:

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 Server 2008 and Windows Vista file information notes

The MANIFEST files (.manifest) and MUM files (.mum) that are installed for each environment are listed separately. MUM and MANIFEST files and their associated security catalog (.cat) files are critical to maintaining the state of the updated component. The security catalog files are signed with a Microsoft digital signature. (The attributes of these files are not listed.)

All supported x86-based versions of Windows Server 2008 and of Windows Vista

All supported x64-based versions of Windows Server 2008 and of Windows Vista

All supported IA-64-based versions of Windows Server 2008

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

Important This section, method, or task contains steps that tell you how to modify the registry. However, serious problems might occur if you modify the registry incorrectly. Therefore, make sure that you follow these steps carefully. For added protection, back up the registry before you modify it. Then, you can restore the registry if a problem occurs. For more information about how to back up and restore the registry, click the following article number to view the article in the Microsoft Knowledge Base: Windows Server 2008 and Windows Vista originally used small audio-data buffers that reduced latency for streaming audio data. This was optimal for high-end USB audio and audio/video applications.

The Windows XP USB audio driver (Usbaudio.sys) requests 10 milliseconds of audio data at a time from the USB stack (buffer size of 10 milliseconds). However, the Windows Server 2008 and Windows Vista USB audio driver requests 4 milliseconds of audio data at a time (buffer size of 4 milliseconds).

After you install this hotfix, the buffer size of the Windows Server 2008 and Windows Vista USB audio driver is set to 10 milliseconds. This is by default. However, you can set the following registry entry to specify a smaller buffer size.

To set the registry entry, follow these steps:

1. Open Registry Editor. To do this, click Start, type regedit in the Start Search box, and then press ENTER.
2. Locate and then right-click the following registry subkey:
   HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\USB\VID_<xxxx>&PID_<yyyy>\<device_instance>\Device Parameters
3. On the Edit menu, point to New, and then click DWORD (32-bit) Value.
4. Type CapturePacketsPerUrb, and then press ENTER.
5. Right-click CapturePacketsPerUrb, and then click Modify.
6. In the Value data box, type an appropriate value for the buffer size of the Windows Server 2008 and Windows Vista USB audio driver, and then click OK.
   
   Note The value that you specify for this registry entry represents the buffer size of the Windows Server 2008 and Windows Vista USB audio driver. After you install this hotfix, the default value is set to 10. You can set this value to a number between 3 and 10.

Additional file information for Windows Server 2008 and for Windows Vista

Additional files for all supported x86-based versions of Windows Server 2008 and of Windows Vista

Additional files for all supported x64-based versions of Windows Server 2008 and of Windows Vista

Additional files for all supported IA-64-based versions of Windows Server 2008