remember, the channels are summed, so a slightly higher level keeps getting added to itself which could show more after they are all added togther. IE: you set both @ -1 but each left mic is 1.2 db higher(ch-1,3,5), something that you might miss with the 680 metering then all the 1.2 get added up making for a 3.6db difference on the 7-8 channel recording.