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Microsoft® Windows® XP and later provide support for GFX (global effects) filtering of an audio stream. Windows XP supports GFX only for USB devices.
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 EQ, 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, 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 Multimedia control panel, the user can do the following:
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 non-accelerated) 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 in order to support GFX filters should be backwards compatible with any earlier versions of Windows that the driver needs to support.