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Journal of the Audio Engineering Society

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2003 November - Volume 51 Number 11

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Papers

Binaural Audio in the Era of Virtual Reality: A Digest of Research Papers Presented at Recent AES Conventions

Authors: Linkwitz, Siegfried

[feature article] This article presents a digest of selected papers from recent AES conventions in the field of binaural or head-related spatial audio reproduction. It specifically excludes multichannel recording and reproduction techniques and wavefield synthesis, which will be covered in a future article.

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Why Is Bass Reproduction from a Dipole Woofer in a Living Room Often Subjectively More Accurate Than from a Monopole Woofer?

Authors: Linkwitz, Siegfried

Letter to the editor

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Comments on `History of Spatial Coding`

Authors: Scheiber, Peter

Letter to the editor

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Acoustical Measurements of Traditional Theaters Integrated with Chinese Gardens

Authors: Chaing, Weihwa; Hsu, Yenkun; Tsai, Jinjaw

Acoustical measurements were taken in three traditional theaters integrated with Chinese gardens. Each theater consisted of a pavilion-like stage inside a courtyard surrounded by covered galleries, walls, or rock piles. The courtyard was generally rectangular in shape. Water, rocks, bridges, walls, and vegetation made the theater space rather irregular. All measurements were taken when the floors were unoccupied and without seats. Analysis showed an average strength G of 4.7 dB, an average early decay time EDT of 0.74 s, and an average early support STE of '9.3 dB.

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Large-Signal Analysis of Triode Vacuum-Tube Amplifiers*

Authors: Abuelma'atti, Muhammad Taher

A mathematical model for the input/output characteristic of a single-stage triode vacuumtube amplifier is presented. The model, basically a cosine-series function, can easily yield closed-form series expressions for the amplitudes of the output components resulting from multisinusoidal input signals to the amplifier. The special case of an equal-amplitude twotone input signal is considered in detail. The results show that, similar to transistor-based amplifiers, the vacuum triode amplifier generates both even- and odd- order harmonic and intermodulation components. The results also show that the amplitudes of these components are strongly dependent on the tube parameters, the biasing voltage, and the amplitudes of the input tones and are not following a general pattern.

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Ultra-High Quality Video Frame Synchronous Audio Coding

Authors: Smithers, Michael J.; Crockett, Brett G.; Fielder, Louis D.

Two methods of coding and delivering ultra-high-quality audio are presented. Both methods are video frame synchronous and editable at common video frame rates (23.98, 24, 25, 29.97, and 30 frames per second) without the use of sample-rate converters. The first is an ultra-high-quality audio coder that exceeds 4.8 on the ITU-R five-point audio impairment scale at a bit rate of 256 kbit/s per channel and at up to three generations of encoding/decoding. The second is an enhanced method of video frame synchronous PCM packing. Specifically the problem of transmitting 48-kHz audio in 29.97-Hz frames is examined.

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The Effect of Nonlinear Distortion on the Perceived Quality of Music and Speech Signals

Authors: Tan, Chin-Tuan; Moore, Brian C. J.; Zacharov, Nick

The effect of various types of nonlinear distortion on the perceived quality of speech and music signals was examined. In experiments 1 and 2, "artificial" distortions were used, including hard and soft symmetrical and asymmetrical peak clipping of various amounts, center clipping, and full-range waveform distortion produced by raising the instantaneous absolute value of the waveform to a power (≠1) while preserving the sign. Subjects were asked to rate the perceived amount of distortion on a ten-point scale (where 1 was most distorted and 10 least distorted). In experiment 1 the distortions were applied to the broadband signals. In experiment 2 the distortions were applied to subbands of the signal. Results were highly consistent across subjects and test sessions. Center clipping and soft clipping had only small effects on the ratings, whereas hard clipping and the full-range distortions had large effects. The subjective ratings were compared to physical measures of distortion based on multitone test signals. A distortion measure, DS, derived from the output spectrum of each nonlinear system in response to a 10-component multitone signal gave high negative correlations with the subjective ratings (correlations were negative as large values of DS were associated with low ratings). A further experiment was conducted using stimuli for which nonlinear distortion was introduced by recording the outputs of real transducers. The output signals were digitally filtered to reduce irregularities in the amplitude/frequency response as far as possible. The results showed moderately strong negative correlations between the subjective ratings and the objective measure DS. It was concluded, that an objective measure of nonlinear distortion based on the use of a multitone signal can predict the perceptual effects of nonlinear distortion reasonably well.

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