Dejan Ciric

• University of Nis

The usage of wavelets is widespread in many fields nowadays, especially in signal processing. Their nature provides some advantages in comparison to the Fourier transform, and therefore many applications rely on wavelets rather than on other methods. The decomposition of wavelets into detail and approximation coefficients is one of the methods to e...

One of the techniques most commonly used for de-noising of audio signals, images or speech is wavelet denoising. However, with regard to de-noising of room impulse responses (RIRs), the usage of wavelets can be hardly found in literature. This paper explores the potentials of applying wavelets for the reduction of negative effects of noise in these...

Serious effects of noise present in room impulse responses (RIRs) on evaluation of room acoustical parameters can be compensated by applying different methods. One of the preferred methods is based on the noise subtraction, RIR truncation and correction for truncation. This paper presents a procedure for calculation of the correction term that shou...

Global Christoffel–Darboux formula for different polynomials has already been used for the filter design. Here, this formula for orthonormal Chebyshev polynomials of the second kind and for two independent variables is applied in generating novel class linear-phase two-dimensional (2-D) finite impulse response (FIR) digital filter functions. In thi...

Noise represents one of the most significant disturbances in measured room impulse responses (RIRs), and it has a potentially large impact on evaluation of the decay parameters. In order to reduce noise effects, various methods have been applied, including truncation of an RIR. In this paper, a procedure for the response truncation based on a model...

This paper presents an audio compression system that applies the sub-band coding (SBC) technique with logarithmic compandors. SBC decomposes signal into the chosen number of frequency bands, which are coded separately. The goal is to design a SBC system that uses quasi-logarithmic quantizers and to find the optimal bit allocation. This would result...

An original analytical method, based on modified Christoffel–Darboux formula, is used in the paper in order to synthesise a linear-phase band-pass finite impulse response (FIR) filter function that can have an effect of Hilbert transformer. New structure of the band-pass FIR filter in recursive realisation, together with the corresponding differenc...

Estimation of speech power spectral density has special importance in speech analysis, synthesis and recognition. It is of practical interest to derive an adequate analytic function that describes speech power spectral density, like the one standardized by CCITT convention. In this paper, the analytical approximation of experimentally obtained spee...

Wavelet analysis is one of the methods for solving difficult engineering problems that enables overcoming some deficiencies of classical Fourier analysis. This paper investigates possibilities for reducing noise in the measured room impulse responses using wavelet transform. In that, an approach based on discrete wavelet transform is applied. The e...

Christoffel–Darboux formula for Chebyshev continual orthogonal polynomials of the first kind is proposed to find a mathematical solution of approximation problem of a one-dimensional (1D) filter function in the z domain. Such an approach allows for the generation of a linear phase selective 1D low-pass digital finite impulse response (FIR) filter f...

In this article, the approximation problem of a continuous analogue filter function of even and odd order is solved mathematically most directly applying the proposed generalised Christoffel–Darboux formula for two continuous orthogonal polynomials (Chebyshev first and second kind) on the equal finite segment of orthogonality in a compact explicit...

In room impulse response measurements, there are some common disturbances that affect the measured results. These disturbances include nonlinearity, noise and time variance. In this paper, the effects of nonlinearities in the measurements with exponential sweep-sine signals are analyzed from different perspectives. The analysis combines theoretical...

Swept sine technique is one of the most used techniques for measurement of the impulse response of acoustical systems including rooms. During its application, some common disturbances, such as noise and distortion, could reduce the quality of the measurement results. Two different noise categories can be distinguished - background noise always pres...

Spherical microphone arrays are used for spatial sound field analysis. Although there are commercially available products, they are not the most suitable for research due to their price and working limits of the embedded software. In those cases it is more convenient to build an own prototype in a lab. In this paper, the analysis of the effects of...

New solutions in construction of transformers in recent years have made the transformers to be seen as modern products whose service life is more than 40 years. However customer's requirements in terms of transformer's noise are increasing and they are sometimes even stricter compared to the standard which prescribes the allowed values of transform...

Power spectral density represents one of important characteristics of speech. The estimation of its value is done using various approaches and algorithms. In this paper, the power spectral density of speech in Serbian language is calculated by applying severel methods. For that purpose,. the speech base is formed in a such way that 8 speakers read...

The approximation problem of a filter function of even and odd order is solved mathematically in this paper most directly applying the proposed Christoffel-Darboux formula for two continual orthogonal polynomials on the equal finite segment. As a result, a linear phase low-pass digital finite impulse response (FIR) filter function is generated in c...

In the room impulse response measurements, one of the common disturbances affecting the measured results is nonlinearity. When maximum length sequences are applied for the measurements, the distortion products are distributed along the estimated impulse response. While this property of maximum length sequences has been widely used in the auditory s...

Addition of dither before the quantization (or requantization) linearizes the quantization characteristic for signals of low levels. However, the dither addition increases overall noise, which is uniformly distributed within the whole frequency range. By transposing a part of that energy into frequency regions where a human ear is less sensitive, t...

Global Christoffel-Darboux formula for four orthonormal polynomials on two equal finite segments for generating linear phase two-dimensional finite impulse response (FIR) digital filter functions in a compact explicit representative form is proposed in this paper. The formula can be most directly applied for solving mathematically the approximation...

The absorption of sound in air represents one of the main problems of the scale model measurements. This absorption, especially at higher frequencies, is considerably greater than the value determined by the law of acoustical similarity between the full scale and the scale model. Different alternatives are applied for compensation of the excess air...

Determination of some important room acoustic quantities is based on backward (Schroeder) integration of a room impulse response. In order to increase the dynamic range of the obtained reverberation decay curve, certain common methods have been adopted. One of the most widely used methods is related to truncation of a room impulse response before t...

One of common procedures applied in the estimation of decay parameters is the backward (Schroeder) integration of a squared room impulse response. This integration results in a reverberation decay function (curve). An inherent characteristic of the backward integration is a bias of the decay late part caused by the cumulative summing of squared noi...

One of common disturbances in the room impulse response measurements is nonlinearity. When maximum length sequence (MLS) method is used, the distortion products are distributed along the impulse response. This property has been widely used in the auditory system applications for characterization of nonlinear systems. However, it has not been exploi...

Information aspect of sound implies the need that sound pressure is observed as an electrical signal. Such a signal can be analyzed and processed. As a consequence, special type of systems with blocks optimized for mathematically intensive operations have been developed. In this paper, digital audio effects are realized and analyzed on DSP processo...

Swept sine technique is one of the most used techniques for measurement of the impulse responses of the acoustical systems including rooms. It uses a swept sine as an excitation signal. During its application, some disturbance, such as noise, could reduce the quality of the measurement results. Two different categories of noise can be distinguished...

A standardized acoustical coupler should enable the calibration of audiometric earphones which ensures that the hearing thresholds determined in the audiometric measurement are independent of the earphone type. This requires that the coupler approximates the average human ear closely. Nevertheless, the differences among earphones as well as between...

Maximum Length Sequence (MLS) technique is a very efficient measurement technique widely used in room acoustics. One of its advantages in comparison to other methods and techniques is transient noise immunity. Namely, the mentioned noise is transformed through the cross-correlation into background noise. Transient noise influence in MLS technique i...

A theoretically obtained optimal Truncation Point (TP) in the Room Impulse Response (RIR) is located at the intersection of the main decay slope and the noise floor. Precise determination of this point is difficult in practice. Namely, the deviation of the RIR decay from the exponential decay can lead to discrepancies in the determined TP from the...

Maximum length sequence (MLS) technique represents widely used technique for measurement of impulse responses. Since the impulse response is extracted by cross-correlation between the excitation signal and measured response, the distortions of these signals can significantly influence the measurement results. Possible distortions of the excitation...

An acoustic coupler should enable calibration of audiometric earphones to be independent of the earphone type. Besides, the coupler should approximate the average human ear as closely as possible. Nevertheless, the differences among earphones as well as between human ear and the coupler affect the results of audiometric measurements. In order to fu...

The integration over discrete squared room impulse response (RIR) leads to the sound pressure level (SPL). However, certain inaccuracies in SPL determination appear as a consequence of influences of finite integration upper limit (UL) and noise. Due to that, these influences are investigated using two types of RIRs: those generated by simulation an...

The sound pressure level (SPL) of the maximum length sequence (MLS) signal can be obtained by integration over the squared room impulse response from zero to infinity. However, this integration in practice is performed over a finite impulse response leading to the inaccuracy in SPL determination. In order to analyse the mentioned accuracy, the infl...

The use of a standardized acoustical coupler should enable a calibration of audiometric earphones which ensures that the thresholds determined in the audiometry will be independent of the earphone type. This requires that the coupler approximates the average human ear closely. Nevertheless, the differences among earphones as well as between human e...

A simple measurement system with a computer as the main unit is developed for the measurements of the characteristics of an anechoic room, such as measurements of the sound?pressure decay in space, the sound?pressure decay in time, and the sound insulation. The measurements are performed in two steps. The room response signals are first recorded an...

Various factors should be optimised in the MLS (maximum length sequence) technique in order to obtain the best results. This paper analyses two of these factors, synchronisation between the start of the excitation signal and of the recording of the response signal used for cross-correlation as well as the stationary sound field setting before the e...

Averaging on various levels has been implemented in the interrupted noise method as well as in the MLS (maximum length sequence) technique. Thus, averaging of the obtained responses, squared pressure decays and logarithmic decays in the interrupted noise method and decay range improvement in the MLS technique are analysed in this paper. The results...

Sadržaj — Modeli prostorija umanjenih dimenzija i danas zauzimaju značajno mesto u modelovanju akustike prostorija. Jedna od najvažnijih aktivnosti koja se obavlja na modelima jesu akustička merenja. Međutim, ova merenja imaju izvesne probleme koje treba prevazići. U radu se ukazuje na specifičnosti i probleme akustičkih merenja u modelima. Posebna...