dBu (Voltage Level)

Formula

Description

dBu is an absolute voltage measurement referenced to 0.7746V RMS, which is the voltage that produces 1 mW into a 600Ω load. The reference comes from the historical 600Ω impedance standard in telephone systems. Professional audio equipment commonly uses +4 dBu (1.228V RMS) as the nominal operating level, providing higher signal levels than consumer equipment for better noise performance. Despite the historical 600Ω connection, modern dBu measurements are made in a voltage-only context without assuming any specific impedance.

Variables

• dBu — Voltage level referenced to 0.7746V RMS (dB)
• V — RMS voltage (V)

Practical Notes

Professional audio standard is +4 dBu = 1.228V RMS. Microphone levels are typically -60 to -20 dBu. Mixer outputs are designed for +4 dBu nominal with headroom to +20 dBu or more. The "u" stands for "unloaded" (or unterminated), distinguishing it from the older dBm which assumed a 600Ω termination. Most modern audio equipment has high-impedance inputs (10kΩ+), making the 600Ω origin irrelevant.