ABSTRACT
Often arbitrarily assigned, in an audio system, it is the ratio between the desired signal level and the extraneous audible material, such as hum, surface scratches, vibrations from components, etc. It is usually expressed in decibels (dB). For instance, an S/N ratio of 50 dB means that the signal is 50 dB louder than the extraneous noise. Obviously the higher the ratio, the better the result, because an overlay of equipment-generated background noise is undesirable in audio recording and playback systems. The noise should be measured using a true RMS type voltmeter over a specified bandwidth, and sometimes weighting filters should be used to account for audibility differences at various frequencies. All these things must be stated for a S/N spec to have meaning, and simply saying a playback device or recorder has a S/N ratio of 70, 80, or 90 dB means nothing, without giving the reference level, measurement bandwidth, and any weighting filers. Note also that a system’s maximum S/N should equal its dynamic range.
