Signal-to-noise ratio (sometimes abbreviated S/N) expresses the relative amount of interference with the signal in a sound system or in any one of its components. In the language of electronics, "noise" is any kind of unwanted signal that intrudes into, or interferes with, the desired signal. In high fidelity, noise takes many forms: the rumble of a turntable, the hum of an amplifier, the hiss of a tape recorder, or atmospheric "static" superimposed on a radio signal. Perhaps, the most consistently unappreciated pleasure of high fidelity is that all these forms of noise are held to a minimum by good equipment, and that the music emerges from a silent background. The signal-to-noise ratio is expressed as the loudness difference (in decibels) between the desired signal (usually measured at the equipment's full rated output under test or at some other standard value) and the interfering noise. In amplifiers, for instance, a specification reading "hum and noise -60 db" means that hum and other noises are at a level of 60 db below the desired signal reproduced at a given output level. A rating of -60 db is good - the higher the figure, the lower the noise. The signal-to-noise figures at high-gain inputs (such as tape-head or phonograph preamplifier) will always be worse than those of lower gain inputs, such as tuner or auxiliary. (Fantel, Hans; The True Sound of Music - A Practical Guide to Sound Equipment for the Home; 1973, E. P. Dutton & Company, Inc., New York)

See Also

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Attenuation
Interference
Modulation
Signal
Signal Attenuation
Signal Conditioner
Signal Gain