RÉSUMÉ
BACKGROUND AND OBJECTIVES: In clinical masking, the plateau is a state in which the non-test ear (NTE) is completely masked by the noise and tone is heard only by the test ear (TE). At least 15 to 20 dB of plateau width is needed to obtain valid threshold. In the study, a part of plateau after initial masking level known as the minimum plateau width (mPW) was determined and compared by a new formula and the plateau searching method. SUBJECTS AND METHODS: Minimum plateau widths of air conduction were obtained in 29 participants with unilateral and 30 participants with bilateral conductive hearing loss (CHL) aged 20 to 45 years old by using step by step plateau method and mPW estimation by the formula between two points of masking diagram [mPW=(N2-N1)-(T2-T1)] and then the mPW of two methods was compared for each frequency. RESULTS: There was no significant difference between the minimum plateau width obtained by the plateau and formula methods for two given point of masking diagram in people with unilateral and bilateral CHL at octave frequencies from 500 Hz to 4,000 Hz. CONCLUSIONS: Threshold obtaining of TE by two tones for two noise levels delivered to the NTE is enough to estimate the mPW between these two noise points and it is not necessary that for clinicians to know the actual values of masking diagram components.