dB expresses a logarithmic ratio, rather than a standalone measure of loudness. For amplitude under the same comparison conditions: ΔdB = 20 log10(A2/A1), so the amplitude multiplier is g = 10^(ΔdB/20). Power ratios use 10 log10 instead. The two formulas are not interchangeable.
| Change | Approximate amplitude multiplier |
|---|---|
| −12 dB | 0.251 |
| −6 dB | 0.501 |
| −3 dB | 0.708 |
| 0 dB | 1 |
| +3 dB | 1.413 |
| +6 dB | 1.995 |
−6 dB means roughly half the amplitude, rather than necessarily half the perceived loudness. Perceived loudness depends on frequency, duration, spectrum, monitoring equipment, and musical context.
dBFS uses digital full scale as its reference. A sample peak with a magnitude of 1 in a normalized convention is 0 dBFS. −12 dBFS is lower than −6 dBFS. A meter reading is not a measurement in watts or analog input voltage; the relationship between dBFS and voltage depends on the interface calibration. dBu, dBV, and dB SPL have different references.
Amplitude and Trim
What changes with Trim at −6 dB?
- Amplitude multiplier
- 0.501×
- Input Peak
- -6.02 dBFS
- Output Peak
- -12.02 dBFS
The output becomes 50.1% of the input amplitude. The waveform shape stays the same.
A sample sine wave with an input Peak of 0.5. Trim multiplies amplitude; clipping that has already happened before the input cannot be restored.