9. How to enable the USB DAC function?

For Mac computers, it is driver-free.

For Windows computers, please make the settings as the followed steps.
1.Install the FiiO DAC driver(Download link: Click here) in the computer first. 
2.Switch the working mode of the M17 to USB DAC mode on the drop-down menu or go to Settings->Mode choose menu to enter the USB DAC mode.
3. Connect the M17 to the computer by the USB port. Select the M17 as the audio input both in the computer and the music app, so it can work.

Notes:
When in the USB DAC mode, the M17 does not support Bluetooth transmitting.