What is the standard definition of noise?

• A. A pleasant sound
• B. Any disagreeable or undesirable sound
• C. A sound with a frequency below 20 Hz
• D. A sound with constant amplitude

Answer: (B)

Noise is any sound that is unwanted or disagreeable to the listener. The key idea isn’t whether a sound is pleasant or loud, but whether it is undesirable in the given context—annoying, distracting, or potentially harmful. That’s why a pleasant sound doesn’t fit, and a sound with a frequency below 20 Hz (infrasonic) isn’t the standard definition of noise. A constant-amplitude sound isn’t necessarily noise either; noise typically has fluctuating amplitude and a broad, non-specific frequency content, often perceived as random or irregular. So the standard definition centers on the sound being unwanted or disagreeable.