Universal Audio Volt 476 Hardware Manual page 13

(12) Mono Button
Press the mono button to route the monitor source direct inputs in mono
instead of stereo. The button lights blue when enabled.
Important: The mono button applies to Volt's hardware inputs only.
(13) Input Meters
The input meters show the level of signal on the inputs.
The red LED lights when the level is near 0 dB. To prevent undesirable
clipping, adjust GAIN so only green and yellow meters light, and the red
LED doesn't light.
(14) Output Meters
The output meters show the level of signal at the monitor and headphone
outputs.The red LED lights to indicate that the level is near 0 dB.
(15) Host indicator
The host indicator is lit blue when Volt is recognized by the computer or
device.