What is the setting of the MASTER OUT ATT. (-12/-6/0 dB) switch upon factory shipment? In what cases should it be switched?

We recommend you to keep the channel level indicator not to exceed 12 dB (to keep the level out of red) to prevent sudden loudness. Please control it with the TRIM knob.
Output will not be distorted with the volume up to 21 dB when [MASTER OUT ATT.] of MASTER OUT is 0 dB.
We recommend you to keep the master level indicator not to exceed 12 dB (to keep the level out of red). Please control it with the MASTER LEVEL knob.
CLIP indicator will quickly blink to indicate internal digital clipping.
Please control at [MASTER OUT ATT.] according to acceptable input level of post-connected device. Set attenuation level of audio output from [MASTER 1] and [MASTER 2] terminals.
Please refer to the the operating instructions for details.