What does an FM signal sound like when received slightly off frequency?

In Frequency Modulation (FM), the audio information is conveyed by variations in the carrier's frequency. The receiver uses a discriminator circuit to decode these frequency swings back into audio. If the receiver is tuned slightly off the center frequency of the transmitted signal, the discriminator cannot properly track the full swing of the deviation. Because parts of the signal fall outside the receiver's filter passband, the resulting audio is clipped and sounds 'scratchy' or distorted. Unlike Single Sideband (SSB) signals, where being off-frequency noticeably changes the pitch of a voice, being off-frequency on FM degrades the audio quality without shifting the pitch.