Stock Android limits the output of most USB audio devices to 43% of their actual output with few exceptions. In order to use the full output of products like the Apple USB-C to 3.5 mm Headphone Jack Adapter (Apple dongle), one must either have an app that only works with a rooted device or use a workaround made possible by USB Audio Player PRO (UAPP).
The workaround is as follows:
- With the USB audio device connect, open UAPP and grant it exclusive control over the USB audio device
- Set the USB audio device’s hardware volume to maximum
- Exit UAPP
This procedure must be followed every time the USB audio device is connected.