To communicate and compare the amount of microphone noise more easily, the electrical noise is filtered to approximate human hearing and converted to an equivalent sound pressure. The microphone is useful only for listening to sound above this equivalent sound pressure, quieter sounds are obscured by the microphone noise. Signal-to-noise (S/N) is a different way to convey the same value. 94 dB SPL is assumed for the signal. Subtracting the microphone self-noise (in dB SPL) from 94dB gives the microphone noise as a signal-to-noise.