Both FAIRCHILD670 mkI and mkII are equipped with a Link that can be operated in 4 different modes :

“LEFT/ RIGHT” mode :
1) Dual Mono with two separate channels and thresholds

“LINK” mode, for Stereo use :
2) Master Left , Slave Right, if you only use the Left Channel Threshold.

3) Master Right, Slave Left, if you only use the Right Channel Threshold.

4) Left + Right Master, with both side-chain Mixed if you use both Threshold Controls.