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The Correlation Between Distortion Audibility and Listener Preference in Headphones

Picture of paper on listener preference & distortion audibility in headphones

Listener Preference & Distortion Audibility in Headphones

The correlation between listener preference and distortion audibility is investigated in this AES paper from Steve Temme, Dr. Sean Olive et al. Five popular headphones with varying degrees of distortion were selected and equalized to the same frequency response. Trained listeners compared them subjectively using music as the test signal, and the distortion of each headphone was measured objectively using SoundCheck. The correlation between subjective listener preference and objective distortion measurement is evaluated and discussed.

Authors: Steve Temme, Sean E. Olive*, Steve Tatarunis, Todd Welti*, and Elisabeth McMullin*            *Harman International
Presented at the 137th AES Conference, Los Angeles 2014

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Listener Preference & Distortion Paper Abstract & Introduction

Abstract
It is well-known that the frequency response of loudspeakers and headphones has a dramatic impact on sound quality and listener preference, but what role does distortion have on perceived sound quality? To answer this question, five popular headphones with varying degrees of distortion were selected and equalized to the same frequency response. Trained listeners compared them subjectively using music as the test signal, and the distortion of each headphone was measured objectively using a well-known commercial audio test system. The correlation between subjective listener preference and objective distortion measurement is discussed.

Introduction
There has been much research published on how a loudspeaker’s linear performance, e.g. frequency, time and directional responses, affects perceived sound quality. However, there is little research published on how non-linear distortion affects perceived sound quality. In recent years, the increasing availability and affordability of high quality headphones and personal digital music
players e.g. MP3 players, has brought high quality music playback to the masses. The transducer performance is critical to listener enjoyment and Dr. Olive and others have presented research on what they believe the target frequency response of the headphone should be for optimum sound quality [1]. The attempt of this research is to determine what level and what kind of distortion is audible and how it affects the perceived sound quality.

Five different pairs of good quality over-the-ear headphones with varying levels of distortion were objectively measured and subjectively rated for their perceived sound quality. First, each headphone was equalized to the same target frequency response. Several different kinds of distortion metrics including harmonic, intermodulation, and non-coherent distortion, were measured for each headphone. A listening test was then conducted where the five headphones were rated by eight trained listeners based on preference and distortion using four short musical excerpts. The program material was selected for wide dynamic and frequency ranges to excite mechanisms in the headphone transducers that would cause distortion.

The different headphones were presented virtually to listeners via binaural recordings of the headphones reproduced through a calibrated low-distortion reference headphone, Stax SR-009. This virtual headphone test method minimized headphone leakage effects, and removed the influence of non-auditory biases (brand, price, visual appearance, comfort, etc.) from listeners’ judgment of sound quality. In this paper, correlations between subjective and objective ratings of distortion are examined (as was done previously [2]) in an attempt to develop an objective metric for measuring distortion audibility in headphones and other loudspeakers. This could possibly be extended to other types of audio devices such as amplifiers.

 

More about Headphone Testing using SoundCheck

Advances in Impedance Measurement of Loudspeakers and Headphones

Impedance measurement is often the sole electrical measurement in a battery of QC tests on loudspeakers and headphones. Two test methods are commonly used, single channel and dual channel. Dual Channel measurement offers greater accuracy as both the voltage across the speaker (or headphone) and the reference resistor are measured to calculate the impedance. Single Channel measurement methods are more commonly used on the production line because they only require one channel of a stereo soundcard, which leaves the other free for simultaneous acoustic
tests. They are less accurate, however, due to the test methods making assumptions of constant voltage or constant current. In this paper we discuss a novel electrical circuit that offers similar impedance measurement accuracy compared to complex dual channel measurement methods but using just one channel. This is expected to become popular for high throughput production line measurements where only one channel is available as the second channel of the typical soundcard is being used for simultaneous acoustic tests.

Authors: Steve Temme and Tony Scott
Presented at the 135th AES Conference, New York 2013

Full Paper