No, I'm not really talking about making these adjustments during a live performance; I mean doing this when you are tweaking your songs, adjusting this and that. You could have a reference decibel level, say, with your Main Volume knob at 50%, max decibel level is not allowed to go over 70db or whatever number you choose.
You would be adjusting via the "Song Volume" button on your keyboard. Uh... I've confused myself... I guess you can Save this parameter in the midi file. If not, you'd have to lower each channel's volume setting.
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Bill
SmallGig.com