The Calm can adjust the startup sound volume of your Mac. You can also silence. In addition you can set the sound volume of after startup. If you are connecting a device to the headphone jack, the setting of the volume of the device will be as same as the settings of the Calm. If the Mac startup sound is increased by connecting the device to the headphone jack, please disconnect the device of the headphone jack. Then install the Calm. You startup sound can be set.