Compatible Amplitude Modulation - Digital or CAM-D is a proposed hybrid digital radio format for AM broadcasting, put forth by the broadcast engineer Leonard R. Kahn.
The system is an in-band on-channel technology that uses the sidebands of any AM radio station. Analog information is still used up to a bandpass of about 7.5 kHz, with standard amplitude modulation. The missing treble information that AM normally lacks is then transmitted digitally beyond this. Audio mixing in the receiver then blends them back together.
Unlike other IBOC technologies like iBiquity's HD Radio, Kahn's apparently does not provide a direct path to all-digital transmissions, nor any multichannel capability. The advantage however is that it takes up far less of the sidebands, thereby causing far less interference to adjacent channels, hence the "Compatible" in the name. The interference problem has plagued HD Radio on AM, along with the fact that it, like CAM-D, is proprietary.
Digital Radio Mondiale, commonly used in shortwave broadcasting, can use less, the same, or more bandwidth as AM, to provide high quality audio. Digital Radio Mondiale requires digital detection circuitry not present in conventional AM radios to decode programming. Special CAM-D receivers provide the benefit of better frequency response and a slow auxiliary data channel for display of station ID, programming titles, etc.