Hi kc402002,
I'm just a newbie to the scanner world but my BCT15X scanner has the option to offset any frequency in a range of either +1, +2,+3, for a higher volume, or -3, -2, -1 for a lower volume, that is programmed into the scanner.
Not sure if this will help you though. It sounds like you're looking for an external device/equipment.
Steve in Vermont