A new modulation scheme for AM sound broadcasting is being studied which allows an additional data signal to be transmitted without significant envelope distortion or increase in bandwidth. The data signals carry information that can be used by specially-equipped receivers for various display and control functions. The proposed radio-data system concerns services for medium or high frequency broadcasting where AM predominates. A real-time implementation of the proposed system using a digital signal processor (TMS 320) is described, and experimental results for sinusoidal envelope modulation are presented. Measurements of the spectrum of the resulting signal show more than 40 dB rejection of out-of-band components, relative to the carrier.