Comparison of distortion products in headphone equalization algorithms for binaural synthesis

Headphone design has traditionally focused on creating a frequency response to make commercial stereo audio sound more natural. However, because of the sensitivity of spatial hearing to frequency-dependent cues, binaural reproduction requires headphones' target spectrum to be as flat as possible. Initial attempts to equalize headphones used a naive inversion of the headphone spectrum, which degraded binaural content because the headphone transfer function (HpTF) changes each time headphones are re-seated. Many different algorithms have been proposed to improve binaural equalization, each of which has been tested over a limited sample of HpTFs. The present study gathered 1550 HpTFs from different institutions into a single dataset for large-scale comparisons of equalization algorithms. A numerical metric was designed to quantify auditory perception of spectral coloration from 'ringing' peaks in the post-equalization HpTF. Using this metric, eight of the most prominent equalization methods have been compared over the aggregate HpTF dataset. High-shelf regularization is shown to outperform all other equalization techniques using either individualized or averaged input spectra. In addition, high-shelf regularization without individual measurements gives less average coloration than direct inversion using individualized equalization.