Marc von Martial
Posts: 10875
Joined: 1/4/2001
From: Bonn, Germany
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I did a quick search. This should help:
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/stream/hh/stream/aud-design_8beb.asp
[QUOTE]DirectSound Hardware-Acceleration and SRC Sliders
Windows 98/Me, and Windows 2000 and later, provide global slider controls for altering DirectSound performance on a system-wide basis. The sliders control the level of hardware acceleration and quality of sample-rate conversion (SRC) that are made available to DirectSound applications.
To locate the DirectSound hardware-acceleration and SRC sliders under Windows XP, for example, follow these steps:
Double-click the Sounds and Audio Devices icon in Control Panel.
Click the Audio tab.
Select a device from the Sound Playback list.
Click the Advanced button.
Click the Performance tab.
At this point, you should see two sliders that are labeled Hardware acceleration and Sample rate conversion quality.
The hardware-acceleration slider has four settings that range from "None" (level 0) on the left to "Full" (level three) on the right. The table below shows the meaning of these settings:
Acceleration level Setting name Description
0 Emulation Forces emulation.
1 Basic Disables hardware acceleration of DirectSound secondary buffers.
2 Standard Enables hardware acceleration of DirectSound secondary buffers but disables vendor-specific property-set extensions.
3 Full Enables hardware acceleration of DirectSound secondary buffers and enables vendor-specific property-set extensions.
Emulation Setting
The Emulation setting above forces DirectSound into emulation mode. In this mode, DirectSound applications run as though no DirectSound driver is present. All mixing is done by DirectSound in user mode, and the resulting audio data is played back through the waveOut API. The result is typically a large increase in latency. Note that after you select this setting, you might need to reboot if you are running a Windows version that is earlier than Windows XP and you want to change to one of the other three settings: Basic, Standard, or Full. This problem has been fixed in the version of DirectSound that ships with Windows XP and later.
Basic Setting
The Basic setting disables hardware acceleration of DirectSound secondary buffers. Under this setting, all DirectSound applications run as though no hardware acceleration is available, regardless of the capabilities of the sound card that is being used. You can use this setting during testing to emulate a sound card that has no DirectSound acceleration. With an adapter such as the OPL, which has no acceleration of DirectSound secondary buffers, this setting has the same effect as the Standard setting.
Standard Setting
The Standard setting enables hardware acceleration of DirectSound secondary buffers but disables vendor-specific extensions such as EAX (Creative Technologies' environmental audio extensions) that are exposed as property sets through the IKsPropertySet interface. On Windows 2000, the Standard setting is selected by default and can be changed only by direct end-user action. This purpose of this behavior is to improve stability and to prevent software from placing the audio system in a state from which it cannot be removed without rebooting.
Full Setting
The Full setting enables full acceleration of DirectSound secondary buffers. This setting also enables property sets for vendor-specific extensions that are exposed through the IKsPropertySet interface. IKsPropertySet extensions include vendor-specific hardware enhancements such as EAX. This is the default setting on Windows 98/Me and Windows XP. Again, for the sake of stability, the default setting can be changed only by direct end-user action.
The table below summarizes the default settings for the hardware-acceleration and SRC sliders for the various Windows releases.
Windows release Default hardware-acceleration setting Default SRC setting
Windows 98 Full Good
Windows 2000 Full Good
Windows Me Standard Good
Windows XP Full Best
In Windows XP, the KMixer system driver uses an SRC algorithm that provides a signal-to-noise ratio of up to 85 decibels when the SRC slider is set to Best.
Built on Wednesday, October 03, 2001[/QUOTE]
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