Using the front panel Input Level and Output Level switches, you may change the operating line level for each of the Quattro stereo pairs. In the “out” position, the Quattro is set to a -10dBV line level. Pressing the input level switch and locking it to the “in” position changes the operating line level to a +4dBu setting.
Each switch affects the line level for one of the input or output stereo pairs, i.e. 1/2 or 3/4. It is possible to have one setting for one of the stereo pairs, and a different setting for the other. This will depend on the operating line level of the device that is attached to that particular input or output.
You can, in fact, have an input set to one line level and the corresponding output set to another, depending on your needs.
Generally speaking, a device that runs at a -10dB line level will have outputs or inputs that are single conductor with a ground, such as RCA jacks, or 1/4” tip-sleeve phone jacks. Devices that run at a +4dB line level will have outputs or inputs that are two conductor with a ground, such as XLR or 1/4” tip-ring-sleeve
jacks.