dBu, dBV and dBFS: what is the difference?
The decibel is not a unit of level on its own. It is a ratio, and every "dB-something" says what the ratio is measured against.
The analogue references
| Unit | Reference | Where you meet it |
|---|---|---|
| dBu | 0.7746 V RMS | Professional line level (+4 dBu nominal) |
| dBV | 1 V RMS | Consumer line level (−10 dBV nominal) |
The 0.7746 V in dBu comes from the old telephone standard: the voltage that delivers 1 mW into 600 Ω, since √(0.001 W × 600 Ω) ≈ 0.7746 V. Modern gear rarely uses 600 Ω, but the voltage reference stuck.
Converting between them is a fixed offset of about 2.2 dB: 0 dBV = +2.22 dBu.
The digital reference
dBFS ("decibels relative to full scale") is digital: 0 dBFS is the largest value a converter can represent. Digital levels are therefore always zero or negative. How much analogue voltage corresponds to 0 dBFS depends on the converter's alignment, for example 0 dBFS = +18 dBu on much European broadcast gear.
Try it
Use the dBu / dBV / Volt converter to move between the analogue references.
Draft: this article was written by an AI assistant and awaits technical review.
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