Click here to purchase the entire book in PDF format. Signal to Noise Ratio (SNR or S/N Ratio) The signal to noise ratio is similar to the dynamic range measurement in that it expresses a difference in dB between the noise floor of a DUT and another level. Unlike the dynamic range measurement, however, the signal to noise expresses the difference between the nominal recommended operating level and the noise floor. Usually, this operating level will be shown as 0 dB VU on the meters of the device in question and will correspond at the output to either +4 dBu or -10 dBV, depending on the device.