A-135-4C is a 4x envelope follower with separately adjustable attack and release times for each channel. The module is designed to derive envelope signals from the four input signals of the A-135-4A, which are then used to control parameters of the A-135-4A via the module A-135-4B. Examples of applications are ducking (i.e. the signal from one channel is used to make another channel more or less quiet), as well as compressor or expander functions. The desired output of the A-135-4C is connected to the respective control input of the A-135-4B and the strength and polarity of the parameter influence is set with the corresponding controller on the A-135-4B.

The A-135-4C module has four inputs for the audio signals and four outputs for the envelope signals. The inputs can be internally normalized to the four audio inputs of the A-135-4A using the switching contacts of the input sockets via a 10-pin connection cable. You can select whether the audio signals are tapped directly from the input sockets of the A-135-4A or after the gain control or after the level VCA (three different plug options). The internal connection cable can also be longer, so that the envelope follower module does not necessarily have to be located near the main module.

If a patch cable is plugged into one of the input connectors of the A-135-4C, the internal connection to the A-135-4A is disconnected and the module can be used for other tasks within the A-100 The four envelope signals generated by the module are indicated by LEDs.