How this calculator works
The decibel compresses multiplicative ratios into an additive scale. A voltage ratio uses a factor of 20 because power is proportional to voltage squared across the same impedance. Positive attenuation denotes loss; negative attenuation denotes gain. Use magnitudes or RMS voltages, not signed instantaneous samples.
Formula
A = 20 log10(Vin/Vout); Vout = Vin × 10^(-A/20). At equal impedance, Pout/Pin = 10^(-A/10).
Worked example
An input of 10 V RMS and output of 1 V RMS has 20 dB attenuation and a power ratio of 0.01 at equal impedance. Halving voltage gives 6.0206 dB attenuation.
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Frequently asked questions
Can attenuation be negative?
Yes. It indicates the output amplitude exceeds the input amplitude.
Why not use 10 log for voltage?
The factor 10 applies to power ratios; voltage squared is proportional to power at equal impedance.
Can the output be zero?
Exactly zero voltage corresponds to infinite attenuation, which has no finite numeric result.