Prevalence of DPOAE fine structure

The distortion product otoacoustic emission (DPOAE) fine structure is revealed when measuring DPOAE with a very fine frequency resolution. It is
characterized by consistent maxima and minima with notches of up to 20 dB depth. In this investigation the DPOAE fine structure was determined for 50 normal hearing humans. The purpose was to test for prevalence of fine structure in normal hearing humans and to analyze the spacing of the periodic ripple structure. The ILO96 system was used, and DPOAEs were measured in a frequency range of f2 running from 1 to 6 kHz with a frequency resolution of 50 to 180 primaries per octave, and using primary levels of L1/L2 = 65/45 dB. The results show that all test subjects show a fine structure. Repeated measurements after 4 weeks show that the maxima and minima locations of the fine structure are very consistent. In most test subjects the fine structure is not prevalent over the entire measured frequency range, the prevalence being rather low at high and low frequencies. Averaged over all test subjects, the ripple spacing increases with increasing frequency from 50 to 200 Hz corresponding to a decrease of 1/8 to 1/16 octaves. These data are comparable to data found in the literature. (PhD scholarship by the Oticon Foundation, STVF framework programme). Supported by STVF/FTP.