Journal of the Audio Engineering Society

2004 April - Volume 52 Number 4


Graphing, Interpretation, and Comparison of Results of Loudspeaker Nonlinear Distortion Measurements

Authors: Voishvillo, Alexander; Terekhov, Alexander; Czerwinski, Eugene; Alexandrov, Sergei

Harmonic distortion and total harmonic distortion may not convey sufficient information about nonlinearity in loudspeakers and horn drivers to judge their perceptual acceptability. Multitone stimuli and Gaussian noise produce a more informative nonlinear response. The reaction to Gaussian noise can be transformed into coherence or incoherence functions. These functions provide information about nonlinearity in the form of "easy-to-grasp" frequencydependent curves. Alternatively, a multitone stimulus generates a variety of "visible" harmonic and intermodulation spectral components. If the number of input tones is significant, the nonlinear reaction may consist of hundreds, if not thousands, of distortion spectral components. The results of such measurements are difficult to interpret, compare, and overlay. A new method of depicting the results of multitone measurements has been developed. The measurement result is a single, continuous, frequency-dependent curve that takes into account the level of the distortion products and their "density." The curves can be easily overlaid and compared. Future developments of this new method may lead to a correlation between curves of the level of distortion and the audibility of nonlinear distortion. Using nonlinear dynamic loudspeaker models, multitone and Gaussian noise test signals are compared with traditional and nontraditional measurement techniques. The relationship between harmonics and intermodulation products in static and dynamic nonlinear systems is analyzed.

Two simple Zobel impedance compensation networks for the lossy voice-coil inductance of a loudspeaker driver are described. Design equations for the element values are given, and a numerical example is presented. The synthesis procedure can be extended to realize general RC networks which exhibit an impedance that decreases with frequency at a rate of -n dec/dec, where 0 < n < 1.

A software system for content-based identification of audio recordings is presented. The system transforms its input using a perceptual model of the human auditory system, making its output robust to lossy compression and to other distortions. In order to make use of both the instantaneous pattern of a recording's perceptual features and the information contained in the evolution of these features over time, the system first matches fragments of the input against a database of fragments of known recordings. In a subsequent step, these matches at the fragment level are assembled in order to identify a single recording that matches consistently over time. In a small-scale test the system has matched all queries successfully against a database of 100 000 commercially released recordings.

The extraction of pitch (or fundamental frequency) information from polyphonic audio signals remains a challenging problem. The specific case of detecting the pitch of a melodic instrument playing in a percussive background is presented. Time-domain pitch detection algorithms based on a temporal autocorrelation model, including the Meddis-Hewitt algorithm, are considered. The temporal and spectral characteristics of percussive interference degrade the performance of the pitch detection algorithms to various extents. From an experimental study of the pitch estimation errors obtained on a set of synthetic musical signals, the effectiveness of the auditory-perception-based modules of the Meddis-Hewitt pitch detection algorithm in improving the robustness of fundamental frequency tracking in the presence of percussive interference is discussed.

[feature] Horns and direct-radiating systems have provided the basis for sound reinforcement for more than a century. Both technologies have benefited from engineering and manufacturing improvements as well as demands for pushing the performance envelope. Trends of fashion have often intersected with engineering development, economics, and even marketplace opportunism. A survey tutorial of the significant developments in transduction, signal transmission, and system synthesis is presented here and discussed in historical perspective.

DSP in Loudspeakers

Authors: Staff, AES

[feature] Loudspeaker systems are getting cleverer thanks to the incorporation of advanced digital signal processing algorithms that can compensate for some of the deficiencies in the transduction process. Various forms of nonlinear distortion may be reduced or it may be possible to get better performance out of smaller units by using electronics to counteract physical inadequacies. Some of these processes can make use of psychoacoustical phenomena, such as a means of extending the perceived bass response without actually reproducing the relevant low frequencies, and it may also be possible to modify the way in which the loudspeaker interacts with the listening room. Finally there are various ways by which it may be possible to engineer an all-digital signal chain, even using digital forms of representation right up to the point where the binary data is converted into an acoustical waveform.

Surround Live Summary

Authors: Ampel, Frederick

[feature] On October 9, 2003 a unique day-long event took place at the Manhattan Center Studio complex’s Grand Ballroom. Surround Live was the first ever comprehensive event devoted exclusively to the creation, production, and reproduction of live performance audio in multichannel surround. Surround Live brought together nearly 250 working professionals from a cross section of the audio industry in a one-day interactive workshop, in conjunction with the AES 115th Convention in New York, to discuss the issues and technological challenges created by presenting music, drama, and theater in full multichannel surround audio formats to a live audience.

Engineering reports

Impedance Compensation Networks for the Lossy Voice-Coil Inductance of Loudspeaker Drivers

Scalable, Content-Based Audio Identification by Multiple Independent Psychoacoustic Matching

On the Detection of Melodic Pitch in a Percussive Background

Standards and Information Documents

AES Standards Committee News


25th Conference Preview, London



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Historical Perspectives and Technology Overview of Loudspeakers for Sound Reinforcement

DSP in Loudspeakers

Surround Live Summary

26th Conference, Baarn, Call for Papers


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