The ratio of the amplitude of the desired signal to the amplitude of noise signals at a given point in time. Note 1: SNR is expressed as 20 times the logarithm of the amplitude ratio, or 10 times the logarithm of the power ratio. Note 2: SNR is usually expressed in dB and in terms of peak values for impulse noise and root-mean-square values for random noise. In defining or specifying the SNR, both the signal and noise should be characterized, e.g., peak-signal-to-peak-noise ratio, in order to avoid ambiguity.