One person's noise may be another person's music, but audiologists say a few factors generally tend to distinguish noise from non-irritating sounds.

The American National Standards Institute has defined noise as: any undesired sound; an erratic, intermittent or statistically random oscillation."Sound is noise when its physical components disturb the relationship between man and his fellow man, and man and his environment. Or, when the acoustic emergency causes undue stress and actual physiological damage," Robert A. Baron writes in his book, "The Tyranny of Noise."

Loudness is often a quality associated with noisy sounds, but there are other less obvious sources of aural annoyance. Extremes of pitch, startling sounds, monotonous repetition of tone and repeated changes in a sound's source of origin can all contribute to noise.

Noise can also hinge on a listener's frame of mind. A sound that is not bothersome when a person is awake or relaxed may turn into "noise" when he or she wants to go to sleep or tries to concentrate.

The human ear is more sensitive to high-frequency sounds than to low-frequency. But low-frequency noise sources, such as transportation vehicles, can be extremely disturbing, even though they may not pose a threat of hearing damage.

The magnitude or intensity of sound is commonly measured in decibels (db), a standard that filters some lower frequencies out of the measurement.

Decibels progress in logarithmical fashion similar to the way the ear perceives sound changes. For example, a 10 decibel sound is 10 times more intense than a 0 decibel sound, while a 20 decibel sound is 100 times more intense than a 0 decibel sound.

The following is a list, compiled by Sound and Vibration magazine, of the decibel levels of some common sounds:

20 - rustling leaves

32 - soft whisper at 5 feet

55 - window air conditioner

60 - conversational speech

69 - vacuum cleaner at 10 feet

80 - ringing alarm clock

85 - level at which hearing damage begins after prolonged exposure

92 - heavy city traffic

98 - lawn mower

100 - 100-cubic-foot air compressor

107 - jackhammer

115 - jetliner 500 feet overhead