Few studies exist on the perception and measurement of nonlinear distortion in headphones. This paper reports the detection thresholds and perceived sound quality from real distortion in headphones. Five different distortion measurements were made on the headphones to determine how well they predict audibility and quality. Music samples were binaurally recorded on six headphones at playback levels ranging from 85 to +110 dBA at 3 dB increments. The recordings were reproduced at a normal playback level (83 dBA) through a reference headphone with low distortion. The headphone recordings were post-processed to remove both level and frequency response differences so only nonlinear distortions and residual noise remained. In a second test, listeners rated the similarity in quality of headphones relative to an undistorted reference and a hidden version of it. The results provide evidence audible distortion in headphones with music occurs at significantly higher playback levels (104 to 112 dBA SPL) than what is considered typical and safe. The percentage of measured THD in the headphone had the highest correlation with the detection thresholds while the non-coherent distortion with music best predicted the
similarity ratings. We discuss the results and the practical implications they might have on future headphone design, testing and measurement.
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