Signal-to-Noise Ratio (SNR)

Signal-to-Noise Ratio (SNR) 訊號雜訊比/訊雜比/訊噪比/信噪比

SNR = (signal power)/(noise power) = P_signal/P_noise
SNR_dB = 10log₁₀(SNR) = 10log₁₀(P_signal)-10log₁₀(P_noise) in decibels (dB)

Therefore, if P_signal > P_noise,

SNR > 1 and SNR_dB > 0 dB.

If SNR_dB < 0, P_signal < P_noise. In other words, when the SNR_dB is negative, the power of the signal is weaker than the power of background noise.

Reference

Signal-to-noise ratio/訊號雜訊比 (Wikipedia)