This is another of Doepfer's series of quad modules containing four identical circuits. These are compact and cost-effective. This one is only 6HP wide and each of the four exponential VCAs has two voltage control inputs (except the fourth one which uses a socket for a "sum" output from all the VCAs. The audio inputs are "normalled" and cascaded together but can be isolatedfrom each other by the use of jumpers, so that each VCA is completely independent, if desired. i think this is an incredibly useful and space-saving module, and as always from Doepfer, great value for money. Get one. Get two!!