Follow the directions below to reset your Apollo x4:
1. Shut down Apollo x4 and computer.
2. Disconnect any cables connected to Apollo x4 except the power cable (this includes disconnecting the Thunderbolt cable). If there are any monitor speakers or headphones connected to Apollo x4, make sure that they are either disconnected or powered off before continuing.
3. While Apollo x4 is powered off press the following buttons - Preamp knob, Polarity and High Pass buttons (see picture below for reference).
4. With the buttons pressed, turn on the power switch to Apollo x4 - hold down the knob/button combo for approximately 10 seconds until the LED lights on the front panel of Apollo x4 stops flashing.
5. Once the LED lights stop flashing you can release all three buttons, shut down Apollo x4 once more, and reconnect all cabling. Reboot the system like normal.