A circuit or system that converts radiofrequency signals into audio or video signals so that the information can be accessed. This is generally accomplished by mixing the modulated radio signal containing the information down to the audio or video frequency band using a nonlinear device or circuit; the process can be carried out directly or by means of an intermediate frequency (see heterodyne reception; direct conversion receiver).

Domestic radios can detect either amplitude-modulated signals or frequency-modulated signals. They are described as AM receivers or FM receivers, respectively. A receiver that has the facility to detect both types of signal is an AM/FM receiver. High-fidelity (hi-fi) radios usually contain additional circuits that are associated with the audiofrequency amplifier and are used to restore the bass response and treble response of the output to that of the original audible source. The bass boost circuit restores the lower audiofrequency signals; the treble compensation circuit acts on the higher audiofrequencies.

Stereophonic radio receivers contain suitable detecting circuits that demodulate stereophonic radio transmissions and produce two outputs, each of which is separately amplified and output to a loudspeaker.

See also reproduction of sound.