Sources of distortion product otoacoustic emissions revealed by suppression experiments and inverse fast Fourier transforms in normal ears

D. Konrad-Martin, Stephen T Neely, Douglas H Keefe, P. A. Dorn, Michael P Gorga

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Primary and secondary sources combine to produce the 2f1-f2distortion product otoacoustic emission (DPOAE) measured in the ear canals of humans. DPOAEs were obtained in nine normal-hearing subjects using a fixed-f2paradigm in which f1was varied. The f2was 2 or 4 kHz, and absolute and relative primary levels were varied. Data were obtained with and without a third tone (f3) placed 15.6 Hz below 2f1-f2. The level of f3was varied in order to suppress the stimulus frequency otoacoustic emission (SFOAE) coming from the 2f1-f2place. These data were converted from the complex frequency domain into an equivalent time representation using an inverse fast Fourier transform (IFFT). IFFTs of unsuppressed DPOAE data were characterized by two or more peaks. Relative amplitudes of these peaks depended on overall primary level and on primary-level differences. The suppressor eliminated later peaks, but early peaks remained relatively unaltered. Results are interpreted to mean that the DPOAE measured in humans includes components from the f2place (intermodulation distortion) and DP place (in the form of a SFOAE). These findings build on previous work by providing evidence that multiple peaks in the IFFT are due to a secondary source at the DP place.

Original languageEnglish (US)
Pages (from-to)2862-2879
Number of pages18
JournalJournal of the Acoustical Society of America
Issue number6
Publication statusPublished - Jan 1 2001


ASJC Scopus subject areas

  • Arts and Humanities (miscellaneous)
  • Acoustics and Ultrasonics

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