The masking-level difference and overall masker level: restating the internal noise hypothesis

Area of Science:

• Auditory perception
• Psychoacoustics
• Hearing science

Background:

• Masking-level difference (MLD) research often measures MLD as a function of masker level.
• Previous findings indicate MLD size decreases as masker level decreases.
• The role of additive internal noise in this masker level dependency has been under-examined.

Purpose of the Study:

• To review and evaluate the additive internal noise explanation for the masker level dependency of the MLD.
• To assess the fit of this explanation to historical and recent MLD data.
• To compare MLD behavior with insert versus supraaural earphones in light of internal noise.

Main Methods:

• Review of existing literature and data on masking-level difference (MLD) as a function of masker level.
• Analysis of how additive internal noise, particularly its interaural decorrelation at low masker levels, influences MLD.
• Comparison of MLD masker level functions obtained with insert phones versus supraaural phones.

Main Results:

• The additive internal noise explanation provides a robust fit to MLD data spanning four decades.
• This explanation accounts for the observed decrease in MLD size as masker level decreases.
• MLD shows less dependence on masker level with insert phones, consistent with lower internal noise.

Conclusions:

• The additive internal noise model effectively explains the masker level dependency of the MLD.
• Lower internal noise levels associated with insert earphones lead to reduced MLD masker level effects.
• The internal noise explanation should be a key consideration in studies measuring MLD as a function of masker level.