dB

A decibel, or dB, is an appraised signal strength in terms of relative loudness heard by the ear. The decibel is 1/10 of a bel, a unit of sound named after Alexander Graham Bell. A change of 1 dB is just detectable as a change in loudness under ideal conditions.

The decibel is a relative unit. When using decibels to specify an absolute sound level, the decibel value must be qualified by a reference level.

The human ear has such a wide range of sound volumes it can hear/tolerate, that we measure this range logarithmically using dB. This is much like the way the strength of an earthquake is measured logarighmically using the Richter scale. The human ear/brain has a threshold of pain at 130 dB. Therefore the human ear/brain has an amazing dynamic range of 130 dB (ratio of 10 trillion to one).

When you have your hearing measured, the result is plotted in dB on an audiogram. The line that results shows how much hearing loss you have at several different frequencies in terms of dB. A loss of less than 20 dB is considered "normal". You can have losses that exceed 100 dB. Because the scale is a logarithmic scale, a 50 dB loss means you've lost a lot more than half of your hearing.

Thanks to Al Winney for suggesting this term.

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