Gain Staging
Definition
Gain staging is the setting of signal levels at each stage of an audio chain, so that the signal stays well above the noise floor of every stage while keeping enough headroom (the margin below clipping) to pass peaks. In digital systems, common practice places the nominal (RMS) level at about −18 dBFS at each stage, which leaves room for peaks. The EBU R68 alignment places 0 dBu at −18 dBFS, and SMPTE RP 155 places +4 dBu at −20 dBFS. In analogue systems, the professional nominal level is +4 dBu; after conversion, it sits 14 dB below full scale with EBU R68 and 20 dB below with SMPTE RP 155. Errors accumulate along the chain, because every stage set too low adds its own noise and every stage set too high adds distortion.
In the field
The usual method is to set the preamplifier gain with the channel fader at unity (0 dB), so that the fader then works around its nominal position. Raising a downstream fader to make up for insufficient input gain amplifies the noise of the earlier stages along with the signal.
Related lessons
Sources
- Alignment level (Wikipedia), EBU R68 : 0 dBu = −18 dBFS ; SMPTE RP 155 : +4 dBu = −20 dBFS · en.wikipedia.org
- Sound On Sound, « What are the reference levels in digital audio systems? » : alignements EBU et SMPTE, réserve au-dessus du niveau nominal · soundonsound.com
- Line level (Wikipedia) : niveau ligne professionnel +4 dBu nominal · en.wikipedia.org
- xaviliz, analog-digital-level-calibration : correspondances EBU R68 et SMPTE RP 155 entre dBu et dBFS · github.com
- elysia, « −18 dBFS is the new 0 dBu » : niveau nominal numérique vers −18 dBFS RMS, réserve pour les crêtes · elysia.com