Decibel (dB)
The logarithmic scale audio uses for level changes: add 6 dB and the waveform amplitude doubles, subtract 6 dB and it halves.
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What it is
A decibel is a logarithmic way to state a ratio between two levels, not a fixed amount of sound on its own. For signal amplitude, a change of about +6 dB means twice the amplitude and -6 dB means half. Audio meters make the ratio useful by naming a reference: dBFS measures against the digital ceiling, while dB SPL measures sound pressure against the threshold-of-hearing reference. The unit is one tenth of a bel, named after Alexander Graham Bell.
Reach for dB whenever you set gain or compare levels. A 3 dB EQ cut, 12 dB of preamp gain, and a peak at -8 dBFS all use the same compact scale, so large ratios fit on a readable meter. Gain changes also add: two stages adding 3 dB each produce a total increase of 6 dB.
Gotcha: 0 dB is not silence. On a dBFS meter it is the maximum possible digital level, while 0 dB SPL is a quiet reference pressure. For scale on the SPL side, ordinary conversation sits near 60 dB SPL, and 85 dB SPL is where hearing-protection rules such as the NIOSH recommended exposure limit start. A bare dB number is incomplete unless you know the reference or that it describes a change. And twice the waveform amplitude does not mean the sound will feel twice as loud to a listener.
Ask AI for it
Create two WAV renders with FFmpeg's volume filter: leave the first at its original level and apply volume=6dB to the second. Run FFmpeg's volumedetect filter on both and report the change in mean and maximum level in dB. If the boosted version would cross -1 dBFS, first apply volume=-6dB to the source and regenerate both renders from that. Do not normalize, compress, or limit either render.