Convert between voltage, dBV, dBu, and dBm. Plus a guide to the confusing world of audio levels.
Convert between dB gain and linear ratios for voltage and power.
dB = 20 × log₁₀(V₂/V₁)
dB = 10 × log₁₀(P₂/P₁)
"Line level" isn't one thing—it's at least three different standards that evolved from different eras and use cases.
| Standard | Nominal | Voltage | Where used |
|---|---|---|---|
| Professional (+4 dBu) | +4 dBu | 1.228 V | Studios, mixers, pro gear |
| Consumer (-10 dBV) | -10 dBV | 0.316 V | Home audio, DJ gear, some synths |
| Broadcast (+8 dBu) | +8 dBu | 1.947 V | Radio, TV broadcast |
A VU meter's "0" is a nominal operating level, not maximum. On pro gear, 0 VU = +4 dBu. The meter is deliberately sluggish (300ms integration time) to show perceived loudness, not peaks.
Pro analog gear typically has 20+ dB of headroom above 0 VU before clipping. That means +4 dBu nominal, but the electronics can handle +24 dBu peaks (~12V!). This headroom is why analog gear sounds "forgiving"—transients aren't crushed.
Digital has no headroom above 0 dBFS—that's absolute maximum. Exceeding it causes hard clipping. The mapping between analog and digital varies by device, but commonly:
This varies wildly between devices. Always check your specific gear's calibration.
Simple voltage reference. 0 dBV = 1V RMS. Used in consumer audio specs.
dBV = 20 × log₁₀(V / 1V)
Professional audio standard. 0 dBu = 0.775V RMS. Why 0.775V? It's the voltage that dissipates 1mW in 600Ω (the old telephone line impedance). The "u" means "unterminated"—the value doesn't depend on actual load impedance.
dBu = 20 × log₁₀(V / 0.775V)
Power reference, requires knowing impedance. 0 dBm = 1mW. In a 600Ω system, 0 dBm = 0 dBu = 0.775V. In a 50Ω RF system, 0 dBm = 0.224V. Only meaningful when impedance is specified.
dBm = 10 × log₁₀(P / 1mW)
dBu and dBV differ by a constant: dBu = dBV + 2.21 dB
This is because 20 × log₁₀(1V / 0.775V) = 2.21 dB
| +4 dBu | = | 1.228V | Pro nominal |
| 0 dBu | = | 0.775V | |
| -10 dBV | = | 0.316V | Consumer |
| 0 dBV | = | 1.000V | |
| +24 dBu | = | 12.3V | Pro max |
| +6 dB | = | 2× voltage |
| +20 dB | = | 10× voltage |
| -6 dB | = | 0.5× voltage |
| -20 dB | = | 0.1× voltage |
| +3 dB | = | 2× power |
| +10 dB | = | 10× power |
Connecting consumer gear to pro inputs: Turn up the input gain, or use a +12dB boost. Some mixers have a "-10/+4" switch for this.
Connecting pro gear to consumer inputs: Pad the signal down ~12dB, or just turn down the output. Watch for clipping on the consumer gear's input stage.
Balanced vs unbalanced: Balanced connections (XLR, TRS) reject noise and are standard in pro gear. Unbalanced (TS, RCA) is fine for short runs. This is separate from level—you can have balanced -10dBV or unbalanced +4dBu.
Impedance matching: Modern audio is "voltage matching" (high Z input, low Z output), not the old 600Ω impedance matching. Don't worry about matching impedances unless you're working with vintage gear or RF.