- Clive Greated
A logarithmic unit used for expressing the difference in level between sounds of different intensity or electrical signals of different power. It is related entirely to the ratio of the two quantities. If two signals have intensities I1 and I2 then their intensity ratio (in dB) is 10 log10 (I2/I1). Differences in level expressed in decibels may be added and subtracted. The intensity level (IL) is defined by comparing the intensity (I) of the sound with a reference intensity (I0), in which case IL = 10 log10 (I/I0). I0 is normally taken as 10-¹² Wm-², corresponding approximately to the lower limit of human hearing. Although the logarithmic intensity level corresponds more closely to the perceived loudness of a sound than would a linear scale, loudness is not directly proportional to intensity level. In fact, for a pure tone, an increase of 10 dB gives rise to a doubling of perceived loudness, corresponding roughly to one step in the musical dynamic (e.g. ...