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 131th AES Convention, San Francisco, 2012

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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

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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

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Evolution of Time-Frequency Analysis Methods and their Practical Applications

Time-Frequency analysis has been in use for more than 20 years and many different Time-Frequency distributions have been developed. Four in particular, Short Time Fourier Transform, Cumulative Spectral Decay, Wavelet and Wigner-Ville have gained popularity and firmly established themselves as useful measurement tools. This paper compares these four popular transforms, explains their trade-offs and discusses how to apply them to analyzing audio devices. Practical examples of loudspeaker impulse responses, loose particles, and Rub & Buzz defects are given as well as a demonstration of their application to common problems with digital/analog audio devices such as Bluetooth headsets, MP3 players and VoIP telephones.

Authors: Pascal Brunet, Zachary Rimkunas and Steve Temme
Presented at the 123rd AES Convention, New York, 2007

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Challenges of MP3 Player Testing

MP3 player audio performance is discussed including measurements of frequency response, phase response, crosstalk, distortion, sampling rate errors, jitter, and maximum sound pressure level with headphones. In order to make these measurements, several measurement techniques and algorithms are presented to overcome some of the challenges of testing MP3 players. We discuss test equipment requirements, selection of test signals and the effects of the encoding on these test signals. A new method for measuring non-coherent distortion using any test signal including music is also presented.

Authors: Steve Temme, Pascal Brunet and Zachary Rimkunas
Presented at the 122nd AES Convention, Vienna, 2007

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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

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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

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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

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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

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Simultaneous measurement of impulse response and distortion with a swept-sine technique

This landmark paper by Angelo Farina discusses the benefits of the Log Sine Sweep (also known as Frequency Log Sweep or Log Chirp), one of the test signals available in SoundCheck.
A novel measurement technique of the transfer function of weakly not-linear, approximately time-invariant systems is presented. The method is implemented with low-cost instrumentation; it is based on an exponentially-swept sine signal. It is applicable to loudspeakers and other audio components, but also to room acoustics measurements. The paper presents theoretical description of the method and experimental verification in comparison with MLS.

Authors: Angelo Farina
Presented at the 108th AES Convention, Paris, 2000

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