The WIM_CLOSE callback message notifies a client that a user-mode driver has finished processing a WIDM_CLOSE message.
A user-mode waveform input driver sends a WIM_CLOSE message to its client, by means of a callback, when the driver finishes processing a WIDM_CLOSE message. The driver sends the message to the client by calling DriverCallback, passing the specified parameters.
The driver sends the WIM_CLOSE message only if the client has previously specified a notification target with a WIDM_OPEN message.
Win32 SDK documentation states that clients receive an MM_WIM_CLOSE message if the notification target is a window handle. WIM_CLOSE and MM_WIM_CLOSE are equivalent.
For additional information, see Notifying Clients from Audio Drivers and Transferring Waveform Input Data.