Decibel (dB) Level Converter
指导
Decibel (dB) Level Converter
The Decibel (dB) Level Converter turns a value entered in one decibel or linear unit into every related representation. Pick a reference type — Sound Pressure Level (SPL), Voltage, or Power — choose what your input is, and the tool computes the equivalent dB readings, the underlying linear quantity (pascals, volts, watts), and the relevant ratios. Conversions follow the standard 20·log₁₀ rule for amplitude/pressure quantities and 10·log₁₀ for power.
如何使用
- Pick a reference type: SPL, Voltage, or Power.
- Enter your value in the Value field.
- Select the unit your value is in (e.g. dB SPL, dBV, dBm, Pa, V, W, or a ratio).
- Read all equivalent values in the output panel.
- 切换 Show formulas used to verify the math, and consult the contextual reference table for typical real-world levels.
特征
- Three reference types – SPL (vs. 20 µPa), Voltage (dBV vs. 1 V and dBu vs. 0.7746 V), and Power (dBm vs. 1 mW and dBW vs. 1 W).
- Linear and logarithmic inputs – Enter either a dB value or a linear value (Pa, V, W) or a raw ratio.
- Pressure ↔ intensity – Automatically computes intensity ratio as (p / p₀)² for plane sound waves.
- Voltage ↔ power – Treats voltage as an amplitude quantity, so power ratio equals the square of the voltage ratio at constant impedance.
- Formula display – Optional inline panel shows the exact formula used for each reference type.
- 参考表 – Common real-world levels for each reference (whisper, conversation, jet engine, line level, Wi-Fi router, etc.) update with the selected reference type.
常问问题
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Why is the formula 20·log₁₀ for some quantities and 10·log₁₀ for others?
Decibels measure a power ratio. When the quantity you have is itself proportional to amplitude (sound pressure, voltage, current), its square is proportional to power, so dB = 10·log₁₀(amplitude²/reference²) = 20·log₁₀(amplitude/reference). Power-like quantities (watts, milliwatts, intensity in W/m²) go straight into 10·log₁₀ because they already represent power.
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What is the difference between dBV and dBu?
Both express voltage on a logarithmic scale, but they use different reference voltages. dBV is referenced to 1 volt RMS, so 0 dBV = 1 V. dBu is referenced to 0.7746 V RMS (the voltage that delivers 1 mW into a 600 Ω load), so 0 dBu ≈ 0.7746 V. As a rule of thumb, dBu ≈ dBV + 2.21.
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What does 0 dB SPL really mean?
0 dB SPL is the threshold of hearing for a healthy young adult at 1 kHz, defined as a sound pressure of 20 micropascals (20 µPa) in air. It is not silence — it is the conventional reference level that all other SPL values are compared to. Sounds below 0 dB SPL still exist; they simply cannot normally be heard.
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Why does doubling the sound pressure add 6 dB but doubling the power add 3 dB?
Doubling pressure doubles the amplitude, and intensity is proportional to amplitude squared, so power quadruples. 10·log₁₀(4) ≈ 6.02 dB, which is the same as 20·log₁₀(2). Doubling raw power gives 10·log₁₀(2) ≈ 3.01 dB. This is why a +6 dB change in SPL corresponds to a 4× power change at the source.
