Custom Audio Effects in Windows Vista Custom Audio Effects in Windows Vista




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How Custom sAPOs are Implemented


Custom sAPOs are implemented as in-process COM objects, so they run in user mode and are packaged in a dynamic-link library (DLL). There are three types of sAPO, based on where they are inserted in the signal processing graph. Each logical device can be associated with one sAPO of each type.

  • A local render effect (render LFX) sAPO processes an audio stream from a particular application just before mixing. If multiple applications are involved, each application has one instance of the LFX sAPO per stream.

  • A local capture effect (capture LFX) sAPO processes an audio stream from an application just before mixing. If multiple applications are involved, each application has one instance of the capture LFX sAPO per stream.

  • A global effect (GFX) sAPO processes the audio stream after mixing. A logical device, such as line out, can have only one instance of the GFX sAPO. If other logical devices such as headphone output or speaker output exist, they get their own instance of the GFX sAPO.


Note: For convenience, the terminology in this white paper refers mostly to output devices. However, the technology is symmetric and works essentially in reverse for input devices. The primary difference is that there is no way to insert a GFX sAPO into the capture graph.

LFX and GFX sAPOs operate on a single input or output stream. They cannot be used in “full-duplex” mode to process both input and output data. The infrastructure is not designed to accommodate effects such as acoustic echo cancellation (AEC) and microphone array processing. With Windows Vista, these types of processing algorithms are located in the application graph, above the audio subsystem. Windows Vista ships with high-quality implementations of both algorithms in that location.

More details on how to implement custom sAPOs are given later in this paper.


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Custom Audio Effects in Windows Vista Custom Audio Effects in Windows Vista

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