Hearing judges ratios: each doubling of power sounds like a similar step, whether from whisper to voice or voice to shout. Decibels encode that by measuring level logarithmically, 10 dB per tenfold power change, roughly 6 dB per doubling of amplitude.
Why the scale is logarithmic
The ear covers an absurd range. The quietest audible sound and the threshold of pain differ by a factor of about a trillion in power. A linear scale would spend six zeros describing a rock concert; the logarithmic scale compresses the whole range into about 120 tidy steps. The formula is simple: dB = 10 × log10(P/P₀), a power measured against a reference power. Every decibel figure is secretly a comparison, and the reference decides which flavor of dB you are reading.
The flavors: dB SPL, dBFS, dBA, LUFS
dB SPL measures sound pressure in air against the threshold of hearing. Conversation sits near 60 dB SPL, a club system near 100, and sustained exposure above 85 starts costing hearing.
dBFS is digital audio’s version: decibels below full scale, where 0 is the hard ceiling of the converter and everything musical lives in negative numbers. A mix might average -14 dBFS with peaks near -1. This is why digital meters read negative; they count headroom spent, down toward the ceiling.
dBA is dB SPL filtered through A-weighting, a curve that discounts the low and very high frequencies the ear is less sensitive to at moderate levels. Noise regulations and handheld SPL meters usually quote dBA, which is why a bass-heavy system can feel louder than its dBA figure admits.
LUFS weights for perceived loudness over time, which is what streaming platforms normalize to.
Landmarks worth memorizing
- 0 dB SPL: threshold of hearing
- 60 dB SPL: conversation
- 85 dB SPL: hearing damage begins with sustained exposure
- 100-105 dB SPL: club front of house
- 120 dB SPL: pain
- 0 dBFS: the digital ceiling, nothing exists above it
- -14 LUFS: common streaming loudness target
The rule for reactive design
Work in dB, not raw amplitude. A fader, a meter, and an eye all expect equal steps to mean equal-feeling changes, and only the logarithmic scale delivers that. Photism’s metering follows the same rule: visual energy tracks level in dB, so a quiet passage breathing and a drop landing both move the picture in proportion to how they feel.