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

When an FM receiver is tuned above or below a signal's frequency, it results in distortion of the signal's audio. This happens because the FM demodulation process is sensitive to the precise frequency of the received signal. If the receiver is not precisely tuned to the carrier frequency of the incoming signal, the demodulator can misinterpret the frequency variations that comprise the audio information, leading to incorrect audio output.

While distortion of the audio can lead to other artifacts, it is primarily the result of improper tuning, which affects how the receiver processes the frequency deviations that encode the audio signal. Tuning errors can cause a variety of issues, including incorrect interpretation of the audio components, making this answer particularly relevant in understanding the importance of correct tuning in frequency modulation systems.