Decibel

Decibels measure a ratio between two levels, which is why a bare number means nothing without knowing the reference. In recording the reference is dBFS, full scale, where 0 dB is the loudest a digital file can go, so every usable level is a negative number. Around 6 dB is a doubling or halving of amplitude, and roughly 10 dB reads to the ear as twice or half as loud. Because the scale is logarithmic, the distance from -60 dB to -50 dB is the same ratio as -20 dB to -10 dB, though only one of them is audible in a quiet room. Compressor thresholds, gain trims and fader moves are all quoted in this unit.