The A-135-4C is a quad envelope follower with adjustable attack and release time for each channel. The main function of the module is to derive four envelopes from the A-135-4A audio input signals. These voltages can be used to control parameters of the main module A-135-4A via the CV input module A-135-4B2. Typical applications are ducking (e.i. the signal of one channel is used to mute another channel more or less), as well as compressor and expander functions. For this the desired envelope output of the A-135-4C is patched to the CV input of the A-135-4B which is assigned to the parameters that has to be modified by the envelope signal. Intensity and polarity of the envelope influence to the parameter in question are adjusted by means of the corresponding polarizer control. The module has four audio inputs and four envelope outputs available. The inputs can be normalled to the inputs of the A-135-4A by means of an internal 10 pin ribbon cable. One can choose between direct input (= input sockets of the A-135-4A), post gain and post main VCA (3 different connectors). The cable can be longer so that the envelope follower module A-135-4C needs not to be mounted next to the main module A-135-4A (e.g. to the row above or below). As soon as a patch cable is connected to an input of the A-135-4C the internal connection to A-135-4A is interrupted and the module can be used independent from the A-135-4A for other applications (e.g. as a simple Attack/Release module with gate signals as inputs or as envelope followers for other signals). The four envelopes generated by the module are displayed by means of LEDs. A-135-4C is not necessary to run the modules A-135-4A/B but is required only for the additional features described above (e.g. ducking, compressing, expanding).