Journal of the Audio Engineering Society

2003 March - Volume 51 Number 3


[feature article] Part One of this article, published in the December 2002 issue, reviewed recent developments in digital audio interfaces, including approaches involving computer network systems. That was concerned principally with streaming audio in production, postproduction, and broadcasting environments; in other words, the transfer of one or more real-time streams of audio data between devices—the digital equivalent of analog signal cables.

Author's Reply to Letter to the editor

Letter to the editor

Loudspeaker Equalizer Design for Near-Sound-Field Applications

Authors: Ser, Wee; Wang, Peng; Zhang, Ming

Loudspeaker equalization is an essential technique in audio reproduction. Conventional equalization schemes focus on dealing with the axial impulse response, and thus cannot provide sufficient off-axis equalization, which is required in near-sound-field applications. A new loudspeaker equalizer is proposed. It addresses this problem and the problem of binaural perceptual difference. Equalizer designs for multiuser and/or multiposition environments are also briefly discussed. These methods have the potential of being applied in practice in the implementation of automobile, TV, or desktop loudspeaker systems.

To measure the variations of the head-related transfer function (HRTF) caused by the acoustical environment near the head, a precisely controlled measurement setup with increased signal-to-noise ratio is needed. Based on the conclusions of an earlier investigation, a fully automatic dummy-head measurement system was installed in an anechoic room. An alternative way of generating a pseudorandom test signal is described as well as the rebuilding of the Brüel & Kjaer turntable for accurate settings of azimuth.

Moving-Horizon Optimal Quantizer for Audio Signals

Authors: Goodwin, Graham C.; Quevedo, Daniel E.; McGrath, David

By analyzing the quantization of audio signals as a deterministic finite-set constrained quadratic optimization problem, a new scheme, called moving-horizon optimal quantizer (MHOQ), is developed. The MHOQ includes a model of the ear's sensitivity to low-level noise power and minimizes directly the perceived error over a finite prediction horizon. Feedback is incorporated by means of the moving-horizon principle. With a prediction horizon equal to 1, the MHOQ reduces to the psychoacoustically optimal noise-shaping quantizer, widely used in practical applications. Larger prediction horizons outperform the noise shaper at the expense of only a small increase in computational complexity.

Signal Representation Including Waveform Envelope by Clustered Line-Spectrum Modeling

Authors: Kazama, Michiko; Yoshida, Kazuaki; Tohyama, Mikio

Clustered line-spectrum modeling (CLSM) around the peaks of interpolated FFT spectrum records has been developed for signal analysis and representation including the signal envelope. The signal waveform, including the envelope, can be represented by components clustered around spectrum peaks. The sinusoidal components at the peaks are estimated by peak picking, whereas the clustered components required in particular for envelope representation can be estimated by obtaining least-squares error (LSE) solutions in the frequency domain, which was originally formulated by Quatieri and Danisewicz and by Maher. Numerical simulation reveals that the basic CLSM algorithm works well, and a narrow-band speech sample or impulse-response type transient-signal analysis shows that acoustic signals that include envelopes can be expressed quite effectively by using clustered components based on CLSM.

Engineering reports

A Moving-Horizon Optimal Quantizer for Audio Signals

Test Signal Generation and Accuracy of Turntable Control in a Dummy-Head Measurement System

Loudspeaker Equalizer Design for Near-Sound-Field Applications

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