Introduction
The input section is the point where signal is introduced into a virtual channel. On the FOH mixer, SAC defines the input source and all Monitor mixers recieve signal via an internal digital split.
Element Description
Channel Disable
The Channel Disable control is only available on the FOH mixer and does what it says. It disables an input channel and stops all processing for the virtual channel. Since the virtual channels on all other mixers are sourced from the FOH mixer, this also disables the input signal and processing for all other mixers.
Channel disable is effectively the same as setting a channel's input source to "Off" without losing the defined input source.
Input Source
Left-clicking on the Input Source control displays a menu with options for stereo devices, mono devices, SAW Studio linked sources, FX sources or the Off state. Channels in the Off state add no load to the SAC audio engine.
Mono Selection
Mono input sources automatically enable the mono button. Turning it off automatically selects the stereo pair the mono channel belongs to. You can merge a stereo source to mono by selecting this button. Clicking the "Mono" label displays a menu of mono summation options. (L+R -6db, L+R, L only, R only, L-R -6db, L-R).
Attenuator
This is a digital gain control, recallable by sessions, channel presets and scenes. The range is -inf to +20db. Attenuation is post A/D conversion however. While it may reduce the metering below clipping in SAC, it does not reduce the level hitting your digital converters and prevent clipping at the source. It is very useful for adding additional clean gain for things such as vocal channels to gain up from a standard preamp volume that doesn't cause clipping with the microphone being used.
Polarity Reverse
This is your standard polarity reverse switch. The default behavior on a stereo channel is to reverse both left and right signals. Clicking the label to the left of the button displays a menu allowing reversal of only the left or right channel.
Swap L/R
Does exactly what it says.