4.26  effective masking level for pure tones. Sound pressure level of a band of noise whose geometric center frequency coincides with that of a specific pure tone that masks the pure tone to 50% probability of detection. The hearing level reference of the masking signal is equal to that of the pure tone. Unit, decibel (dB).

Annotation 1      Effective masking level is analogous to hearing level, i.e., a measure of sound on a physical scale, independent of the ear under test.

Annotation 2      On a normally hearing ear the amount of effective masking, abbreviated EM, is equal to the number of decibels that a given band of noise shifts a pure tone threshold. For example, 20 decibels EM would produce a threshold shift of 20 decibels when the band of noise and pure tone are presented simultaneously to the same ear.

Annotation 3      Typically, the output of a pure tone audiometer for bands of noise is calibrated in effective masking level.

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