Journal of the Audio Engineering Society

2007 July/August - Volume 55 Number 7/8


Modeling of Loudspeaker Systems Using High-Resolution Data

Authors: Feistel, Stefan; Ahnert, Wolfgang

The need for high-resolution loudspeaker data is evaluated in detail, in particular complex data in their original impulse response or frequency response formats, and how a new data format proposed earlier can be used for storing this and other information required to describe a complex loudspeaker system adequately. Prediction results for several loudspeaker models are compared based on different spectral and spatial resolutions. Calculations are also compared against measurements for different loudspeaker types, such as multiway loudspeakers, clusters, and line-array systems. Finally the advantages of more precise predictions are discussed with respect to increasing requirements regarding computer performance and data storage.

The design of panning functions for surround sound systems with nonuniform loudspeaker layout is considered. It is shown that theoretical solutions exist which are interpolants for nonuniform sampling of periodic functions. However, these solutions produce large interference effects for positions far from the array center, and they are sensitive to phase and magnitude mismatches between loudspeakers. Robust solutions approximate a double complementarity property in which the weights and squared weights sum to 1 for each source angle. A least-squares method is developed for developing robust panning functions which produces a more consistent sound-field directionality than those produced by matching parameters at the origin.

An investigation into the measurement of the thresholds of detection of modal Q factors in rooms at low frequency is measured. Key features of the approach taken include the use of music rather than test tones or noise as program material, and the manipulation of damping conditions for a range of modes over a broad low-frequency bandwidth as opposed to the control of one modal artifact within an array of surrounding uncontrolled resonances. It is shown that the detectability of Q-factor changes is directly proportional to the reference Q, and is weakly dependent on the presence and level of higher frequency reverberations. A threshold value of Q = 16 is suggested, below which further changes are unlikely to be detected.

Presenting sounds in virtual environments requires filtering free-field signals with head-related transfer functions (HRTF). HRTFs describe the filtering effects of pinna, head, and torso measured in the ear canal of a subject. The measurement of HRTFs for many positions in space is a time-consuming procedure. To speed up the HRTF measurement, the multiple exponential sweep method (MESM) was developed. MESM speeds up the measurement by overlapping sweeps in an optimized way and retrieves the impulse responses of the measured systems. MESM and its parameter optimization are described. As an example of an application of MESM, the measurement duration of an HRTF set with 1550 positions is compared to the unoptimized method. Using MESM, the measurement duration could be reduced by a factor of four without a reduction of the signal-to-noise ratio.

Analysis, Synthesis, Voice

Authors: Staff, AES

[Feature] Advances in sound analysis and synthesis for musical applications have led to more realistic emulations of natural sounds, as well as the potential for creating new instruments. In this article we review recent AES convention papers that exemplify some of the most interesting developments in this field, concentrating in particular on a series of papers on vocal or singing synthesis from the team at the Universitat Pompeu Fabra in Barcelona delivered at the AES 121st Convention last year in San Francisco. At the outset, however, we describe two nonvocal synthesis approaches: one that can be used to improve the versatility and efficiency of physical modeling and another that has been employed to resynthesize the sound of a Chinese instrument known as the ehru. At the end of the article we describe two systems for analyzing vocal performances and singing quality.

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