Signal to noise ratio is a specification that measures the level of the audio signal compared to the level of noise present in the signal. Signal to noise ratio specifications are common in many components, including amplifiers, phonograph players, CD/DVD players, tape decks and others. Noise is described as hiss, as in tape deck, or simply general electronic background noise found in all components.
How is it Expressed?
As the name suggests, signal to noise ratio is a comparison or ratio of the amount of signal to the amount of noise and is expressed in decibels. Signal to noise ratio is abbreviated S/N Ratio and higher numbers mean a better specification. A component with a signal to noise ratio of 100dB means that the level of the audio signal is 100dB higher than the level of the noise and is a better specification than a component with a S/N ratio of 90dB.
Why is it Important?
Unfortunately, all components add some level of noise to an audio signal but it should be kept as low as possible. Analog components, such as amplifiers, tape decks and phonograph players generally have a lower signal to noise ratio than digital components, such as CD and DVD players but the goal is still to keep noise as low as possible. As an example, a signal to noise ratio for tape deck or phonograph player is typically about 60dB-70dB, while it is common for a CD player to have a S/N Ratio of 100dB or higher. S/N Ratio is important, but should not be used as the only specification to measure the sound quality of a component.
Courtesy : http://stereos.about.com/od/faqs/f/SNratio.htm
