Windows communicates with audio device drivers through messages sent to the driver. The driver processes these messages with its wodMessage, widMessage, modMessage, midMessage, or auxMessage entry-point function. The function used depends on the type of device the driver supports. Drivers can also send messages to client applications with the DriverCallback function.
This section contains an alphabetical list of all messages that can be received and sent by audio device drivers. Each message name contains a prefix, identifying the type of the message. The following list identifies the prefixes used for audio device driver messages:
| Prefix | Description |
| WODM | Sent by MMSYSTEM to a waveform output driver's wodMessage function. |
| WIDM | Sent by MMSYSTEM to a waveform input driver's widMessage function. |
| MODM | Sent by MMSYSTEM to a MIDI output driver's modMessage function. |
| MIDM | Sent by MMSYSTEM to a MIDI input driver's midMessage function. |
| AUXDM | Sent by MMSYSTEM to an auxiliary audio device driver's auxMessage function. |
| WOM | Sent by waveform output drivers to notify client applications. |
| WIM | Sent by waveform input drivers to notify client applications. |
| MOM | Sent by MIDI output drivers to notify client applications. |
| MIM | Sent by MIDI input drivers to notify client applications. |
A message consists of three parts: a message number and two DWORD parameters. Message numbers are identified by predefined message names. The two DWORD parameters contain message-dependent values.