The dBu unit has its origins in early telephony where 600-ohm impedance was standard. At 600 ohms, 0.775 volts produces exactly 1 milliwatt of power. While modern audio equipment no longer uses 600-ohm impedances, the 0.775V reference point was retained as the definition of 0 dBu. Professional audio equipment operates at a nominal level of +4 dBu, meaning the standard operating level is 1.228 volts RMS. This higher operating level provides better signal-to-noise ratio compared to consumer equipment, which typically operates at -10 dBV (0.316V RMS). The approximately 12 dB difference between professional and consumer levels is why you need level matching when connecting different equipment classes. Understanding dBu is essential when setting gain structure. Each device in an audio chain has an input sensitivity and a maximum output level, both specified in dBu. Proper gain staging ensures that nominal signals sit well below the clipping point while staying well above the noise floor. For example, a mixing console might have a maximum output of +24 dBu and a noise floor of -90 dBu, giving 114 dB of dynamic range. If the nominal operating level is +4 dBu, there is 20 dB of headroom above nominal and 94 dB of signal-to-noise ratio. SonaVyx's transfer function measurements work in the relative domain, so the actual voltage levels do not affect frequency response shape. However, understanding dBu is important when interpreting signal levels displayed on equipment meters and setting proper gain structure before measurements.