Seyyed Jalal Sameni - Department of Audiology, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran
Ahmad Daneshi - Research Center of otolaryngology, Head and Neck Surgery, Hazrat-e-Rasool Hospital,Iran University of Medical Sciences, Tehran, Iran
Akram Pourbakht - Department of Audiology, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran
Aliakbar Tahaee - Department of Audiology, School of Rehabilitation Sciences, Iran University of Medical Sciences, Tehran, Iran

In clinical masking techniques, generally, noise is presented to the nontest-ear when obtaining the test-ear threshold by pure tone stimulus. Based on noise and tone conditions, masking diagram ideally contains three parts: undermasking, plateau and overmasking. Based on audiometer calibration for tone and noise, changes are in a similar way at undermasking and overmasking parts, but in the plateau section, the pure tone threshold remains stable following noise changing ( actual threshold ). Therefore by choosing two points on he masking diagram and using [ (N2-N1) – (T2-T1) ] formula, the minimum plateau width can be estimated between them. N1 and N2 stands for noise values and T1 and T2 are tone values at points 1 and 2 of masking diagram respectively. It was believed that given the characteristics of any two points the minimum plateau width between them can be estimated, whatever the amount of noises are closer together, the plateau width would be more accurate. The purpose of this paper is to estimate the minimum plateau width by the formula that extracted from masking diagram and express its relative benefits in clinical practice.

Masking Diagram, minimum Plateau Width, Pure tone Audiometry & [(N2-N1) – (T2-T1)] formula