Abstract: A customer controlled gain circuit allows a customer to control the transmission amplifier gain in a trunk circuit by means of multifrequency signals. The trunk circuit contains a multifrequency receiver which receives and decodes gain control commands. The commands are applied to a bidirectional shift register containing a single circulating bit. One gain command causes the bit to shift in one direction while another gain command causes the bit to shift in the other direction. The bit appearing at the outputs of the shift register drives a plurality of FET gate circuits which switch various feedback paths in the trunk transmission amplifier.