The 32-bit versions of Microsoft Windows Server 2003 and Windows XP provide support for global effects (GFX) filtering of an audio stream. These operating systems support GFX filters only for USB audio devices. Hardware vendors have the option of providing GFX filters to augment the capabilities of their USB audio devices.

GFX filters that are designed to run in Windows XP and Windows Server 2003 are unlikely to run in later versions of Windows. In particular, Windows Vista does not support GFX filters. Instead, it supports global effects in the form of audio processing objects (APOs). For more information about APOs, see the WinHEC 2003 presentation titled Windows Longhorn Audio Architecture on the  audio technology page on the WHDC Web site.

A GFX filter can apply an audio-signal transform to the final audio mix that is rendered by an audio device. The effect is global because it affects all of the streams that are combined to form the final mix. Examples of these effects are equalization, bass enhancement, and speaker correction.

A GFX filter can also process the signal that is captured by an audio device. The GFX filter is inserted into the capture stream before any other processing of the audio signal.

A GFX filter is packaged as an AVStream minidriver with an associated INF file. For more information about INF files, see Device Installation Files.

A typical GFX filter implements a digital signal transformation that is designed for a specific audio hardware device (for example, to compensate for the response characteristics of a particular set of speakers). The manufacturer of the audio hardware typically provides the GFX driver. When installing a GFX driver, Windows enables the GFX filter and automatically configures it to begin processing the audio signal that is sent to the specified hardware.

Through the Windows multimedia control panel (Mmsys.cpl), the user can do the following:

• Enable or disable a GFX.
• Select among several GFX filters if more than one GFX is available that is designed for the audio hardware in question. A GFX driver's INF file specifies the target hardware for the GFX.

Windows uses no more than one GFX on each audio device. Windows keeps track of GFX configurations on a per-user basis.

GFX filters can be designed for audio-capture devices as well as for audio-rendering devices. For example, the manufacturer of a microphone array might provide a GFX filter to process the input signals from the array.

A GFX filter typically serves as a host-based (or nonaccelerated) enhancement of hardware and is hardware-specific. For example, when a user plugs in USB speakers, a particular GFX filter might automatically load for those speakers. During this process, Windows restores the GFX filter configuration and settings that it saved when the speakers were used previously.

GFX filters should not be used to implement virtual audio devices. For example, a GFX cannot be used to create a composite, four-channel audio device from two independent stereo audio devices.

Any modifications that a vendor makes to an adapter driver to support GFX filters should be backwards compatible with any earlier versions of Windows that the driver needs to support.

Windows Server 2003 and Windows XP support GFX filters only in 32-bit versions of the operating system. GFX filters do not work in 64-bit systems.

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