Abstract: A system connectable into standard television receiver systems for converting predetermined channels thereof to audio only channels and detecting selection of the predetermined channels to cause blanking of the picture tube at individual receivers in the system. The antenna or cable input is altered by supplying a carrier with audio, code and horizontal sync information at a frequency corresponding to that of an unused channel. A tone decoder is responsive to the code and horizontal sync information to cause blanking of the display while the audio information is reproduced in normal manner.