Interacoustics AC40 Instructions For Use Manual page 32

AC40 Instructions for Use - US
Masking Level Difference Test
MLD refers to the improvement in speech intelligibility in noise when a tone is presented in and out of
phase respectively. It aims to assess central auditory function but peripheral changes may also affect the
MLD.
The auditory system has the ability to perceive differences in timing of a sound reaching the two ears.
This helps to othe ar low frequency sounds that reach the ears at different times due to the longer wave
length.
It is measured by simultaneously presenting a 500 Hz interrupted and narrow band noise at 60 dB to both
ears in phase andfinding the threshold. Then the phase of one of the tones is inversed and the threshold
is found once again. The improvement in sensitivity will be greater in the out-of-phase condition. The MLD
equals the difference between the in-phase and out-of-phase thresholds or more formally the MLD may
be defined as the difference in dB between the binaural (or monaural) in phase condition (SO NO) and a
particular binaural condition (e.g. Sπ NO or SO Nπ).
Function Key
10
11
12
16
17
Description
othe ars in phase
Noise in phase and signal in reversed phase.
Signal is in phase and the noise in reversed phase.
Start MLD test.
Stop MLD test.
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