WaveOutSetVolume -

hwo
Handle to an open waveform-audio output device. This parameter can also be a device identifier.
dwVolume
New volume setting. The low-order word contains the left-channel volume setting, and the high-order word contains the right-channel setting. A value of 0xFFFF represents full volume, and a value of 0x0000 is silence.
If a device does not support both left and right volume control, the low-order word of dwVolume specifies the volume level, and the high-order word is ignored.

If you want a function:

Code:

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Public Function MakeLong(ByVal highWord As Long, ByVal lowWord As Long) As Long
  MakeLong = highWord * &H8000& + lowWord
End Function

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