INFO: WDM Acoustic Echo Cancellation (AEC) Filter Drivers Are Broken on Windows 98 and Windows 98 SE (243429)

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The Windows 98 DDK shows the WDM audio AEC (vendor-supplied) filter driver in the WDM audio device-driver stack, in the "Architecture Overview" section. AEC filter drivers are a subset of global effects filters. AEC filter drivers do not work correctly on the Windows 98 original release and on Windows 98 SE. The WDM filter graph is not correctly enumerated by the operating system with the AEC filter. Furthermore, the AEC filter is not called in its DriverEntry kernel-mode function.

Microsoft Development is aware of the problem and is working on a solution for a future release of the operating system.

For Windows 98 original release, you must use the older Windows 95 VxD plus 16-bit Installable audio driver model and include your AEC functionality directly into the VxD or the 16-bit adapter driver. The Windows Hardware Quality Lab (WHQL) will only logo audio drivers based on the VxD plus DRV model for Windows 98.

For Windows 98 SE, you must use the WDM driver model and include the AEC functionality in the adapter driver layer. It is not possible to install a global filter between Kmixer.sys and Portcls.sys. The process of building the WDM filter graph is Microsoft proprietary technology and it is not documented.

The ability to install WDM global effects filters is planned for a future release of the operating system.