In-Vehicle Audio System Distortion Audibility versus Level and Its Impact on Perceived Sound Quality

As in-vehicle audio system output level increases, so too does audio distortion. At what level is distortion audible and how is sound quality perceived as level increases? Binaural recordings of musical excerpts played through the in-vehicle audio system at various volume levels were made in the driver’s position. These were adjusted to equal loudness and played through a low distortion reference headphone. Listeners ranked both distortion audibility and perceived sound quality. The distortion at each volume level was also measured objectively using a commercial audio test system. The correlation between perceived sound quality and objective distortion measurements is discussed.

Authors: Steve Temme, Listen, Inc. and Patrick Dennis, Nissan Technical Center North America, Inc.,
Presented at the 141st AES Convention, Los Angeles, CA 2015

Full Paper

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

Full Paper

 

 

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

Measurement of Harmonic Distortion Audibility Using A Simplified Psychoacoustic Model – Updated

A perceptual method is proposed for measuring harmonic distortion audibility. This method is similar to the CLEAR (Cepstral Loudness Enhanced Algorithm for Rub & buzz) algorithm previously proposed by the authors as a means of detecting audible Rub & Buzz which is an extreme type of distortion[1,2]. Both methods are based on the Perceptual Evaluation of Audio Quality (PEAQ) standard[3]. In the present work, in order to estimate the audibility of regular harmonic distortion, additional psychoacoustic variables are added to the CLEAR algorithm. These variables are then combined using an artificial neural network approach to derive a metric that is indicative of the overall audible harmonic distortion. Experimental results on headphones are presented to justify the accuracy of the model.

Authors: Steve Temme, Pascal Brunet and Parastoo Qarabaqi
Presented at the 51st AES Conference, Helsinki, Finland, 2013

Full Paper

Measurement of Harmonic Distortion Audibility Using A Simplified Psychoacoustic Model

A perceptual method is proposed for measuring harmonic distortion audibility. This method is similar to the CLEAR (Cepstral Loudness Enhanced Algorithm for Rub & buzz) algorithm previously proposed by the authors as a means of detecting audible Rub & Buzz which is an extreme type of distortion[1,2]. Both methods are based on the Perceptual Evaluation of Audio Quality (PEAQ) standard[3]. In the present work, in order to estimate the audibility of regular harmonic distortion, additional psychoacoustic variables are added to the CLEAR algorithm. These variables are then combined using an artificial neural network approach to derive a metric that is indicative of the overall audible harmonic distortion. Experimental results on headphones are presented to justify the accuracy of the model.

Authors: Steve Temme, Pascal Brunet and Parastoo Qarabaqi
Presented at the 133rd AES Convention, San Francisco, 2012

Full Paper

Practical Implementation of Perceptual Rub & Buzz Distortion and Experimental Results

In a previous paper [1], we demonstrated how an auditory perceptual model based on an ITU standard can be used to detect audible Rub & Buzz in loudspeakers using a single tone stimulus. In this paper, we discuss a practical implementation using a stepped sine sweep stimulus and present detailed experimental results on loudspeakers including comparison to human listeners and other perceptual methods.

Authors: Steve Temme, Pascal Brunet and Brian Fallon
Presented at the 129th AES Convention, San Francisco, 2010

Full Paper

Practical Measurement of Loudspeaker Distortion Using a Simplified Auditory Perceptual Model

Manufacturing defects in loudspeaker production can often be identified by an increase in Rub & Buzz distortion. This type of distortion is quite noticeable because it contributes an edgy sound to the reproduction and is annoying because it often sounds separate or disembodied from the fundamental signal. The annoyance of Rub & Buzz distortion is tied intimately to human perception of sound and psychoacoustics. To properly implement automated production-line testing of loudspeaker Rub & Buzz defects, one has to model or imitate the hearing process using a sufficiently accurate perceptual model. This paper describes the results of a Rub & Buzz detection system using a simplified perceptual model based on human masking thresholds that yields excellent results.

Authors: Steve Temme, Pascal Brunet and D.B. (Don) Keele
Presented at the 127th AES Convention, New York, 2009

Full Paper

A New Method for Measuring Distortion using a Multitone Stimulus and Non-Coherence

A new approach for measuring distortion based on dual-channel analysis of non-coherence between a stimulus and response is presented. This method is easy to implement, provides a continuous distortion curve against frequency, and can be used with a multitone stimulus, noise, or even music. Multitone is a desirable test signal for fast frequency response measurements and also for assessing system nonlinearities. However, conventional single-channel multitone measurements are challenging because the number of intermodulation tones grows rapidly with the number of stimulus tones and makes it extremely difficult to separate harmonics from intermodulation products. By using dual-channel measurement techniques, only well-known, standard signal processing techniques are used, resulting in simplicity, accuracy and repeatability.

Authors: Steve Temme and Pascal Brunet
Presented at the 121st AES Convention, San Francisco, 2006

Full Paper

Higher Order Harmonic Signature Analysis for Loudspeaker Defect Detection

Loudspeaker assembly faults, such as a rubbing voice coil, bent frame, loose spider, etc., have traditionally been detected using experienced human listeners at the end of a production line. Previous attempts to develop production measurement systems for on-line testing typically analyze only low-order harmonics for the primary purpose of measuring total harmonic distortion (THD), and thus are not specifically designed to detect defective rub, buzz, and ticking sounds. This paper describes a new method wherein the total energy of high-order harmonics groups, for example, 10th through the 20th or 31st through the 40th, are measured and analyzed. By grouping high-order harmonics and resolving their respective total energies, distinct signatures can be obtained that correlate to the root cause of audible rub and buzz distortions (Temme, 2000). The paper discusses loudspeakers tested with specific defects, as well as results of a computer-based electroacoustic measurement and analysis system used for detection.

Authors: Dan Foley, Dr. Robert Celmer, Benjamin Sachwald, James Anthony, Tony Pagliaro, Shane Thompson
Presented at the 117th AES Convention, San Francisco, 2004

Full Paper

Enhancements for Loose Particle Detection

During loudspeaker production, particles may become trapped in the loudspeaker motor and voice coil vicinity, resulting in a distinctive defect that is easily heard, but difficult to detect by traditional test and measurements. We found that a Sine Sweep Stimulus followed by a High Pass Filter and RMS Envelope Analysis efficiently detected Loose Particles and Rub & Buzz defects. The remaining problem is how to reduce the effect of background noise, and get more reliable results. Statistical descriptors such as Crest Factor, Skewness, and Kurtosis are first investigated. Experimental results are given and the different tools are compared. New enhancements are described that increase effectively the overall immunity to background noise and discrimination of the method.

Authors: Pascal Brunet and Steve Temme
Presented at the 116th AES Convention, Berlin, 2004

Full Paper

Loose Particle Detection

During the loudspeaker manufacturing process, particles may become trapped inside the loudspeaker, resulting in a distinctive defect that is easily heard but difficult to measure. To give a clearer view of the problem, Time-Frequency maps are shown for some defective loudspeakers. Based on this analysis, a reliable testing procedure using a swept-sine stimulus, high-pass filter, and RMS-envelope analysis is presented. Further possible enhancements and applications of the method are listed.

Authors: Pascal Brunet, Evan Chakroff and Steve Temme
Presented at the 115th AES Convention, New York, 2003

Full Paper