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A ratio based measure of the comparative amount of some quality, usually sound level, power or voltage, relative to some reference amount. It is often qualified to indicate what property is being compared i. e. dB(A), dB(v) etc. e. g. One might talk about a signal to noise ratio of 80 dB(v). This would be a comparison between the amplitude of the signal (which we want to hear) and the noise (which we don't). In this case the signal voltage becomes the reference point, (whatever the actual value was) and would be called 0 dB(v), the noise voltage (whatever the actual value was) would therefore be 80 dB(v) smaller. The logarith mic nature of the decibel allows us to compare two values of enormously different magnitudes with conveniently small numbers. e. g. the limits of hearing in terms of absolute pressure level cover the range from 20µPa to 200,000,000 µPa. Any arithmetic on this basis is quite tedious. The same range expressed in dB SPL is 0 -140 dB SPL. Much more convenient. |
