Signal-to-noise ratio describes the ratio of useful information to false or irrelevant information. It is an engineering term for the ratio between the magnitude of a signal (meaningful information) and the magnitude of background noise. Because many signals have a very wide dynamic range, SNRs are often expressed in terms of the logarithmic decibel scale.
If there is a great deal of ambient sound (noise) within the recording environment, the noise floor will be high, and the noise level will be high. Noise in the audio can also be introduced by the recording equipment or system itself.
Signal-to-Noise ratios are closely related to the concept of dynamic range. Where dynamic range measures the ratio between noise and the greatest un-distorted signal on a channel, SNR measures the ratio between noise and an arbitrary signal on the channel.
Commercial tools are available for audio file analysis.