What is the result of tuning an FM receiver above or below a signal’s frequency?

In an FM (Frequency Modulation) receiver, the discriminator or demodulator circuit is designed to decode frequency variations perfectly when centered precisely on the incoming carrier frequency. If you tune the receiver slightly off-frequency, either above or below, the signal falls onto the non-linear portion of the receiver's filters. This off-center tuning results in a garbled, distorted audio output rather than a clean voice. Distractors like "change in audio pitch" or "generation of a heterodyne tone" apply to SSB (Single Sideband) or CW (Morse code) receivers, where changing the dial directly changes the audio frequency you hear.