In order to ensure compatibility with a wide range of headphones, including very sensitive IEMs and low sensitivity full-sized headphones, the HA-2 makes use of two different volume controls: a digital volume control within the DAC itself, and an analogue potentiometer. When used together, the digital volume control can be used to lower the output level from the DAC, and the analog volume control can be used to more finely tune the volume level. Using both volume controls in conjunction with each other is especially useful when connecting IEMs and other sensitive headphones to the HA-2.

The way in which you utilise the HA-2's digital volume control depends on the device that you connect to the HA-2.

When an iOS device (iPhone, iPad, iPod Touch) is connected to Input A, the HA-2 informs the iOS device that it has hardware volume control capabilities and maps the iOS device's software volume control to the HA-2's internal, 32-bit volume control. Using this method, the iOS device still outputs bit-perfect audio and allows for finer volume control adjustment than what the HA-2's analogue volume control provides on its own, without any degradation of audio fidelity. This is particularly useful with IEMs and other sensitive headphones. 

For Android devices connected to Input B, you will need to utilise music playback software such as USB Audio Player PRO, which will allow you to indicate that a hardware volume control is available. Once the Android device's playback software is configured to recognise the HA-2's hardware volume control, it will output bit-perfect audio to the HA-2 and the Android device's volume control will be mapped to the HA-2's 32-bit volume control, allowing for finer volume control adjustment when using IEMs and other sensitive headphones.