0 dBm is 1 milliwatt; it implies an impedance context unlike dBu

dBm expresses electrical power referenced to 1 milliwatt (0 dBm = 1 mW). In the early days of audio, impedances were standardized at 600 Ω, so 0 dBm corresponded to a specific voltage (≈0.775 V into 600 Ω). Modern equipment is not impedance-matched, so dBm is ambiguous unless the load impedance is stated. dBu was introduced to replace dBm for voltage-based measurements: 0 dBu = 0.775 V regardless of load impedance. dBu is now standard in professional audio specs. dBV is referenced to 1 V (0 dBV = 1 V RMS). Consumer equipment typically uses –10 dBV; professional equipment uses +4 dBu — a difference of approximately 11.8 dB.

Examples

0 dBu = 0.775 V RMS. +4 dBu (pro nominal) = 1.23 V RMS. –10 dBV (consumer nominal) = 0.316 V RMS. The gap between consumer and pro nominals is about 11.8 dB.

Assessment

Convert –10 dBV to dBu. Explain why comparing a console spec in dBu to a consumer device spec in dBV requires a conversion factor.