The MODM_SETVOLUME message requests a user-mode MIDI output driver to set the volume level for the specified device.
Parameters
uDeviceId
Device identifier (0, 1, 2, and so on) for the target device.
uMsg
MODM_SETVOLUME
dwUser
Device instance identifier.
dwParam1
A DWORD containing the volume setting.
dwParam2
Not used.
Return Value
The driver should return MMSYSERR_NOERROR if the operation succeeds. Otherwise it should return one of the MMSYSERR or MIDIERR error codes defined in mmsystem.h. See midiOutSetVolume return values in the Win32 SDK.
Comments
A client sends the MODM_SETVOLUME message by calling the user-mode driver’s modMessage entry point, passing the specified parameters.
Support for this message by user-mode drivers is optional. If the driver supports MODM_SETVOLUME, it must support MODM_GETVOLUME.
The volume value is specified by dwParam1 as follows:
| Channel | Portion of dwParam1 Used |
| Left channel | Low word |
| Right channel | High word |
| Single channel | Low word |
A value of zero is silence, and a value of 0xFFFF is full volume.
The kernel-mode driver might not support the full 16 bits of volume control and can truncate the lower bits. However, the original value requested with AUXDM_SETVOLUME should be returned with AUXDM_GETVOLUME.
Typically, the user-mode driver calls DeviceIoControl to send the kernel-mode driver an IOCTL_MIDI_SET_VOLUME control code.
Only drivers for internal synthesizer devices can support volume level changes. Drivers for MIDI output ports should return a MMSYSERR_NOTSUPPORTED error for this message.