The nonlinearities of audio devices can be emulated by means of a nonlinear convolution method, which is based on a particular case of the Volterra series called the Diagonal Volterra series. The Volterra kernel characterizes the nonlinear audio device being tested. Since the behavior of a nonlinear audio system may be influenced by input signal level and since Volterra kernels themselves depend upon the level of the input signal, a numerical and experimental method is presented that approximates the kernels for a continuous range of levels with a limited number of measurements. The model can be extended to handle an arbitrary order of nonlinearities to better emulate the harmonics of low and medium frequencies. This approach is particularly useful for such devices as a tube preamplifier.
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This study investigates the importance of both the auditory and visual modalities when evaluating subjective quality. Bimodal experiments comprising audiovisual and unimodal presentations were used to explore the interaction between modalities. Audio stimuli of varied degradation were coupled with both actual loudspeakers of different visual appearance and scaled photographs of the same loudspeakers. As would be expected, the factor audio had the strongest influence on quality in the audiovisual session. However, in visual only presentations, the factor visual was statistically significant. This indicates that when presented in isolation, the differences between the visual stimuli are perceived clearly and are judged to be substantial but become obscure in the presence of audio stimuli. From a product design perspective, the results suggest that the modalities are independent and that a change in subjective quality in either modality would combine linearly.
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For field recordings and user-generated content recorded on phones, tablets, and other mobile devices, poor audio quality arises in part from nonlinear distortions caused by clipping and limiting at pre-amplification stages and by dynamic range control. Based on the Hearing Aid Sound Quality Index (HASQI), a single-ended method to quantify perceived audio quality in the presence of nonlinear distortions has been developed. Validations on music and soundscapes yielded single-ended estimates within ±0.19 of HASQI on a quality range from 0.0 and 1.0. Perceptual tests were carried out to validate the method for music and soundscapes. HASQI has also been shown to predict quality degradations for processes other than nonlinear distortions including additive noise, linear filtering, and spectral changes. By including these other causes of quality degradations, the current model for nonlinear distortion assessment could be expanded.
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When sound is modulated at frequencies up to 20 Hz, the sensation is that of fluctuation strength. At faster amplitude variations, the sensation is that of roughness. This report describes a new model for calculating fluctuation strength based on equivalent rectangular bandwidth. By using 75 filter channels on the ERB number scale, the total fluctuation strength is calculated by weighting, filtering, and adding the generalized modulation depth (GMD) in each channel. The model changes the way that GMD is converted into specific fluctuation strength. Using an ERB number scale instead of Bark scale provides other advantages. The calculated results using the new model are more consistent with subjective ratings with an RMS error that is decreased by 90% and correlation coefficients are increased by 20%. The proposed model can be used for both narrow and wideband noises.
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When binaural audio signals containing directional cues are presented with loudspeakers, the listener should still be able to localize sound images and experience a realistic three-dimensional sound environment. Because acoustic crosstalk between loudspeaker channels degrades performance, it is necessary to preprocess the binaural signals with a crosstalk cancellation system. However, a limited sweet spot is still a challenge especially when the head is laterally misaligned. To increase the robustness of the reproduction system, a direct multidrive array configuration with multiple control points is combined into the optimal source distribution strategy. The research goal is to find a good trade-off between the crosstalk cancellation performance and a high tolerance to head misalignment. Both simulations and experiments demonstrate the efficacy of the method, and the system is well suited to large display devices.
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Specialists in music-induced hearing disorders and hearing protection gathered in Denmark to share the latest research in the field. Topics included personal music players, music festivals, and the use of ear plugs.
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With the increasing pace at which technology changes and the shifting landscape of the forensic sciences, the need for forensic examiners to remain informed and current with research is obvious. It is no longer possible for forensic work to be conducted in isolation, and it is only through collaboration and exchange of ideas that the forensic sciences will truly be strengthened. Stay tuned for upcoming AES conferences on audio forensics as well as regularly offered workshops and tutorials on the topic at AES conventions.
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