dBFS, dBu, dBV — Decibel Reference Levels
The decibel scales used in audio, how they relate, and why the same '−18 dB' can mean different things.
The decibel is a relative unit. Saying "−6 dB" is meaningless without specifying relative to what. In audio, three reference levels come up constantly:
- dBFS — decibels Full Scale (digital).
- dBu — decibels relative to 0.775 V (analogue, professional).
- dBV — decibels relative to 1 V (analogue, consumer/semi-pro).
Each is a different anchor for "0 dB," and the relationships between them matter when you're routing signal between the analogue and digital worlds.
Convert between dB scales →dBFS — The Digital Scale
In digital audio, 0 dBFS = the maximum possible signal level. Nothing can be louder. Every signal is at a negative dBFS value, with louder signals approaching 0 dBFS.
- 0 dBFS — the digital ceiling. Above this, samples are clipped.
- −18 dBFS — typical mix-bus calibration level for individual tracks.
- −24 dBFS — broadcast and post-production standard reference level.
- −60 dBFS — quiet noise level.
- −96 dBFS — the noise floor of 16-bit audio.
Almost all digital meters and faders in DAWs are dBFS-based.
dBu — Professional Analogue
dBu is referenced to 0.775 V RMS. This odd voltage comes from the legacy of telephone-line power calculations — historically, 0.775 V across 600 Ω equals 1 milliwatt.
- +4 dBu — professional line level. Mixing consoles, studio outboard gear.
- 0 dBu — reference (0.775 V).
- −10 dBV ≈ −7.78 dBu — semi-pro line level (more on this below).
Pro audio gear traditionally operates around +4 dBu nominal.
dBV — Consumer / Semi-Pro Analogue
dBV is referenced to 1 V RMS. Used in consumer gear (CD players, audio interfaces' instrument inputs) and many "semi-pro" devices.
- 0 dBV — reference (1 V).
- −10 dBV — consumer line level standard.
If you connect consumer gear (−10 dBV) to professional gear (+4 dBu), the levels won't match — you've got roughly 12 dB of mismatch to deal with.
The Conversion Reality
A signal at +4 dBu enters your audio interface. Where does it land in dBFS? It depends on the interface's calibration.
A typical professional interface calibrates so that +4 dBu = −18 dBFS. That's the most common convention. But some interfaces calibrate +4 dBu to −20 dBFS, others to −14 dBFS, etc.
You usually can't "fix" the calibration without firmware or hardware control, so you live with what your interface gives you.
Why This Matters in Practice
Headroom planning. If your interface calibrates at +4 dBu = −18 dBFS, then a +4 dBu line-level signal recording without clipping has 18 dB of headroom before hitting digital ceiling. That's good. A signal averaging −10 dBu has roughly 26 dB of headroom — also good.
Gain staging. Knowing your reference levels lets you set gain consistently. A vocal preamp set to give an average +4 dBu output should hit roughly −18 dBFS in the DAW. If it's hitting −6 dBFS, your preamp is producing more than +4 dBu — likely +18 dBu or so — and you're using up headroom needlessly.
Connecting consumer gear. A −10 dBV CD player into a +4 dBu console input sounds quiet. Most modern audio interfaces have switchable line/instrument inputs that handle the conversion, but be aware when you're outside that.
Quick Conversion Table
| dBu | dBV | dBFS (typical, +4 dBu = −18 dBFS) | |-----|-----|------------------------------------| | +4 | +1.78 | −18 | | 0 | −2.22 | −22 | | −10 | −12.2 | −32 | | −20 | −22.2 | −42 |
Common Mistakes
Treating dBFS as if it were absolute SPL. A signal at −18 dBFS doesn't have a fixed loudness. It depends on the playback chain (interface gain, preamp gain, speaker sensitivity, monitor level). dBFS measures only the digital signal level relative to digital full-scale.
Confusing peak and RMS dBFS. Two signals can both peak at −6 dBFS but have very different perceived loudness. RMS or LUFS is the better metric for loudness; dBFS is best for headroom planning.
Ignoring reference-level differences when patching outboard. Sending a +4 dBu hardware compressor's output back into your interface's "instrument" input (designed for −10 dBV / Hi-Z signals) can overload it.