Custom sAPOs are installed with the audio device driver and linked to specific Plug and Play hardware ID. This ensures that a hardware manufacturer can specify the LFX and GFX sAPOs for an audio device and be confident that they will work well together.
Each Plug and Play hardware ID can be associated with only one GFX and one LFX sAPO. However, if developers require variable behavior that is based on different stream or device characteristics, an sAPO can contain multiple DSP algorithms internally that can be used exclusively or together.
Modern PCs normally have separate logical devices for headphone, line out, Sony/Philips Digital Interface (SPDIF) out, speaker out, and so on. When there are multiple logical devices, each one can have its own LFX and GFX sAPO.
As with drivers, custom sAPOs must go through the Windows Logo Program signing process. There are two ways to submit sAPOs to WHQL for signing:
An sAPO that is associated with a custom driver should be submitted with the driver package.
An sAPO that is linked by an INF to one of the Windows Vista UAA class drivers can be submitted separately.
An sAPO commonly provides a user interface (UI) that allows a user to configure the effects. This UI can, for example, allow the user to select from several different signal processing algorithms. Microsoft provides a configuration UI for the standard Windows Vista sAPOs. If a custom sAPO has user-accessible settings, the manufacturer must provide an appropriate configuration UI. The configuration UI is installed with the device driver and is associated with the sAPO by registration.
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