The VU4 is a FOUR CHANNEL VU Meter panel that fits into four V-Rack slots.
The INPUT D-sub feeds the main input and the INSERT D-sub feeds the alternate input, selected by the front panel "IN" button. Additionally, the INPUT d-sub is internally MULTED to the OUTPUT D-sub, eliminating the need for Y cables and external mults.
The REF level is also selectable by the front panel "REF" switch. It selects between the 2 sets of front panel VU calibration pots.
The VU meters are illuminated with white LEDS, eliminating the need for bulb replacement.