An online algorithm for echo cancellation, dereverberation and noise reduction based on a Kalman-EM Method

Many modern smart devices are equipped with a microphone array and a loudspeaker (or are able to connect to one). Acoustic echo cancellation algorithms, specifically their multi-microphone variants, are essential components in such devices. On top of acoustic echos, other commonly encountered interference sources in telecommunication systems are reverberation, which may deteriorate the desired speech quality in acoustic enclosures, specifically if the speaker distance from the array is large, and noise. Although sub-optimal, the common practice in such scenarios is to treat each problem separately. In the current contribution, we address a unified statistical model to simultaneously tackle the three problems. Specifically, we propose a recursive EM (REM) algorithm for solving echo cancellation, dereverberation and noise reduction. The proposed approach is derived in the short-time Fourier transform (STFT) domain, with time-domain filtering approximated by the convolutive transfer function (CTF) model. In the E-step, a Kalman filter is applied to estimate the near-end speaker, based on the noisy and reveberant microphone signals and the echo reference signal. In the M-step, the model parameters, including the acoustic systems, are inferred. Experiments with human speakers were carried out to examine the performance in dynamic scenarios, including a walking speaker and a moving microphone array. The results demonstrate the efficiency of the echo canceller in adverse conditions together with a significant reduction in reverberation and noise. Moreover, the tracking capabilities of the proposed algorithm were shown to outperform baseline methods.

Reducing the harmful effects of noise on the human environment. Sound insulation of industrial skeleton enclosures in the 10–40 kHz frequency range

Purpose The purpose of the research is to work out a method for determining the sound insulation of acoustic enclosures for industrial sources emitting noise in the frequency range of 10–40 kHz and apply the method to measure the sound insulation of acoustic enclosures build of different materials. Methods The method is developed by appropriate adaptation of techniques applicable currently for sound frequencies of up to 10 kHz. The sound insulation of example enclosures is determined with the use of this newly developed method. Results The research results indicate that enclosures (made of polycarbonate, plexiglass, sheet aluminium, sheet steel, plywood, and composite materials) enable reducing the sound pressure level in the environment for the frequency of 10 kHz by 19–25 dB with the reduction increasing to 40–48 dB for the frequency of 40 Hz. The sound insulation of acoustic enclosures with a sound-absorbing material inside reaches about 38 dB for the frequency of 10 kHz and about 63 dB for the frequency of 40 kHz. Conclusion Some pieces of equipment installed in the work environment are sources of noise emitted in the 10–40 kHz frequency range with the intensity which can be high enough to be harmful to humans. The most effective technical reduction of the associated risks are acoustic enclosures for such noise sources. The sound pressure level reduction obtained after provision of an enclosure depends on its design (shape, size, material, and thickness of walls) and the noise source frequency spectrum. Realistically available noise reduction values may exceed 60 dB.

ANALYSIS OF PREPARED ACOUSTIC BOARDS FROM NATURAL WASTE MATERIALS USING ACTRAN SOFTWARE AND ITS APPLICATION

The investigations focus on analyzing acoustic enclosures intended for noisy Chemical Engineering equipment made out of natural waste materials namely corn cobs, corn stovers and banana stalks using Actran Software with the parameters of study being the comparison between different dimensions of enclosure and material properties of different substances used. Upto 50 Hz frequency, there was no evident distinction in the Pressure-map between two dimensions of enclosures, while beyond 50 Hz, there was a difference with the larger enclosure encountering greater pressure intensities as well as greater ranges of pressure intensities. In the frequency range of 40 Hz - 75 Hz for the smaller enclosure and 30 Hz - 65 Hz for the larger, there was a significant effect of the changing material properties on the sound absorbing ability of the enclosure. When the two plots of enclosures for changing material properties were compared, some amount of instability in the graphs of the three materials was encountered at higher frequencies in the case of the larger enclosure. Upon analyzing the results, banana stalks showed better sound absorption potential followed by corn cobs and corn stovers at frequencies in the range 40 Hz - 70 Hz.

ANALYSIS OF PREPARED ACOUSTIC BOARDS FROM NATURAL WASTE MATERIALS USING ACTRAN SOFTWARE AND ITS APPLICATION

The investigations focus on analyzing acoustic enclosures intended for noisy Chemical Engineering equipment made out of natural waste materials namely corn cobs, corn stovers and banana stalks using Actran Software with the parameters of study being the comparison between different dimensions of enclosure and material properties of different substances used. Upto 50 Hz frequency, there was no evident distinction in the Pressure-map between two dimensions of enclosures, while beyond 50 Hz, there was a difference with the larger enclosure encountering greater pressure intensities as well as greater ranges of pressure intensities. In the frequency range of 40 Hz - 75 Hz for the smaller enclosure and 30 Hz - 65 Hz for the larger, there was a significant effect of the changing material properties on the sound absorbing ability of the enclosure. When the two plots of enclosures for changing material properties were compared, some amount of instability in the graphs of the three materials was encountered at higher frequencies in the case of the larger enclosure. Upon analyzing the results, banana stalks showed better sound absorption potential followed by corn cobs and corn stovers at frequencies in the range 40 Hz - 70 Hz.

ANALYSIS OF PREPARED ACOUSTIC BOARDS FROM NATURAL WASTE MATERIALS USING ACTRAN SOFTWARE AND ITS APPLICATION

The investigations focus on analyzing acoustic enclosures intended for noisy Chemical Engineering equipment made out of natural waste materials namely corn cobs, corn stovers and banana stalks using Actran Software with the parameters of study being the comparison between different dimensions of enclosure and material properties of different substances used. Upto 50 Hz frequency, there was no evident distinction in the Pressure-map between two dimensions of enclosures, while beyond 50 Hz, there was a difference with the larger enclosure encountering greater pressure intensities as well as greater ranges of pressure intensities. In the frequency range of 40 Hz - 75 Hz for the smaller enclosure and 30 Hz - 65 Hz for the larger, there was a significant effect of the changing material properties on the sound absorbing ability of the enclosure. When the two plots of enclosures for changing material properties were compared, some amount of instability in the graphs of the three materials was encountered at higher frequencies in the case of the larger enclosure. Upon analyzing the results, banana stalks showed better sound absorption potential followed by corn cobs and corn stovers at frequencies in the range 40 Hz - 70 Hz.

Shape Optimization of Acoustic Enclosures Based on a Wavelet–Galerkin Formulation

The problem of the shape optimization of acoustic enclosures is investigated in this paper. A general procedure, comprising a Wavelet–Garlerkin formulation and a so-called vertex-driven shape optimization is proposed to deal with the general problem of internal sound field prediction and the optimization of the boundary shape. It is shown that, owing to the compactly supported orthogonal property and the remarkable fitting ability, Daubechies Wavelet can be used as a global basis to approximate the unknown sound field on a relatively large interval globally instead of piecewise approximation like most of element based methods do. This feature avoids meshing the boundary of the enclosure, although vertex points are needed to define the boundary shape, whose positions keep updating during the shape optimization process. A rectangular enclosure is used as benchmark to assess and validate the proposed formulation, by investigating the influence of some key parameters involved in the formulation. It was shown that the sound pressure along the entire boundary of the rectangular enclosure can be accurately approximated without meshing. The same enclosure with an inner rigid acoustic screen is then used to reduce the sound pressure level within a chosen area through optimizing the shape of the screen, which shows the remarkable potentials of the proposed approach as a shape optimal tool for inner sound field problems.