Journal of the Audio Engineering Society

2006 July/August - Volume 54 Number 7/8


A Robust and Computationally Efficient Speech/Music Discriminator

Authors: Barbedo, Jayme Garcia Arnal; Lopes, Amauri

A New method for discriminating between speech and music signals is introduced. The strategy is based on the extraction of four features, whose values are combined linearly into a unique parameter. This parameter is used to distinguish between the two kinds of signals. The method has achieved an accuracy superior to 99%, even for severely degraded and noisy signals. Moreover, the low dimensionality of the feature space, together with a very simple information-merging technique, has resulted in a remarkable robustness to new situations. The low computational complexity of the method makes it appropriate for applications that demand real-time operation. Finally excellent resolution for the segmentation of audio streams is achieved by manipulating the analyzed data properly.

Vibrations of Loudspeaker Cones in the Transitional Range

Authors: Zhang, Zhi-liang; Cheng, Chang-jun

The vibration of the loudspeaker conical diaphragm is analyzed in the transitional frequency range, where the bending waves appear on the cone’s outer part and with increasing frequency gradually cover the entire diaphragm. The displacement patterns in the transitional range are described analytically and numerically along with characteristic frequency equations and the axial admittance. The solution of the equations shows a strong coupling between longitudinal and bending motions. For practical applications, the resonance spacing formula is derived as well as the expression for the first nonbending frequency, which may be considered the theoretical upper limit of the loudspeaker frequency response.

The current state of the art of virtual reality allows a user to interact with computergenerated visual worlds and provides a high level of realism. The immersion can be increased significantly by simulating in addition the corresponding room acoustics. A correct acoustical impression is reached by the reproduction of binaural signals and at present already satisfies high demand, but for interactive systems it is mostly limited to sources located in the free field, that is, the filters used for computation are applicable for anechoic environments only. Current real-time-capable room acoustical simulations for virtual environments are mostly based on the principles of geometrical acoustics. However, these approaches do not provide an exact reproduction of a room’s sound properties under real-time conditions because of high computation demands, and they are therefore limited to the simulation of just plausible sound fields. Hence faster algorithms are required to further enhance the room acoustical simulation. A modification of the commonly known image source method is presented, which reduces the computation demands of this highly time-expensive approach remarkably. Binary space partitioning trees are used for a fast determination of audible image sources, and an efficient data structure with respect to the real-time auralization process is introduced. Thus a faster determination of the binaural room impulse response is obtained, which is essential for a real-time-capable auralization process. In addition, geometrical relations are used more efficiently to prevent the generation of redundant image sources and to increase the performance of this algorithm. Furthermore, experiments have been carried out to show the current hardware limitations for this modified image source method.

[Engineering Report] Cumulative spectral analysis (CSA) of transient decaying signal portions is an effective approach to detecting spectral distortion and to determine quickly the principal resonant frequency of a public-address system before it starts howling. Spectral distortion, so-called coloration, due to periodic delays in a feedback loop, which might cause howling of the loop, could be detected by observing a spectral-accumulation process of the signals. CSA was originally proposed by Berman and Fincham for transient analysis of loudspeakers. The cumulative spectral process is investigated by introducing a spectral accumulation function into CSA, called cumulative harmonic analysis (CHA), so that the spectral accumulation process might be visualized effectively. The spectral accumulation effect of signals or impulse responses revealed by CSA is a little less than that found when using CHA. Consequently while a spectral-frequency distribution of the dominant frequency components picked up by CHA for decaying speech-signal portions clearly displays the coloration due to feedback speech signals, it can nevertheless be only slightly perceived by listening. Thus frequency distribution analysis by CHA or by conventional CSA for short decaying segments of signal samples can be useful in the blind prediction of the howling frequency without detailed specifications of the transfer functions and the original input signals under in situ conditions. As future work is concerned, it is necessary to investigate how long an observation interval would be required, and what kind of accumulation function is effective to predict howling frequencies. In particular, simulation experiments for multiple input and output systems, including time-variant closed loops under reverberation conditions, would be necessary for evaluating the proposed method from a practical point of view.

Digital Radio Broadcasting

Authors: Staff, AES

[Feature Article] In December 2004 we reported on recent developments in the world of digital radio, highlighting systems that had been growing in importance both for terrestrial and satellite-based delivery of digital audio to stationary and mobile receivers. We now offer a summary of the current situation with terrestrial digital radio broadcasting in the U.S., based on the in-band, on-channel (IBOC) system, including information on the various initiatives to introduce surround sound into the equation.

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