A software-controlled audio mixer allows applications to control various aspects of the audio mix, such as the relative volume level of each audio source. To write a mixer device driver, first create the initialization part of the driver-the part that includes the LibEntry, WEP, and DriverProc entry-point functions. Next, create the mxdMessage entry-point function and the support code required to implement the driver. Be sure to process all of the required messages for mixer device drivers. For each message you process, use the information provided by the reference at the end of this chapter to ensure you did everything required to correctly process the message.