int MusHandleSetFreqOffset(musHandle handle, float offset);
It defines a frequency offset that is added to the frequency generated by the sound data, before the sound is generated, on the channels associated with the specified sound handle.
The handle must be a sound handle returned by MusStartSong(), MusStartSongFromMarker(), MusStartEffect(), or MusStartEffect2(). If a handle of zero is supplied, this function will always return zero.
The offset is a floating point value, with 1.0 being a semitone. A limited range of values should be applied using this function (dependant on sample rate). The default frequency offset value for all channels is 0.
Number of channels to which the frequency offset has been applied.
void SetEngineOffset(float offset)
{
MusHandleSetFreqOffset(engine_handle, offset);
}