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1

Study on the Effectiveness of Monte Carlo Filtering when Correcting Negative SEA Loss Factors

Nieradka Paweł, Dobrucki Andrzej

Archives of Acoustics

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2023

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Vol. 48, No. 2

201--218

EN

The power injection method (PIM) is an experimental method used to identify the statistical energy analysis (SEA) parameters (called loss factors – LFs) of a vibroacoustic system. By definition, LFs are positive real numbers. However, it is not uncommon to obtain negative LFs during experiments, which is considered a measurement error. To date, a recently proposed method, called Monte Carlo filtering (MCF), of correcting negative coupling loss factors (CLFs) has been validated for systems that meet SEA assumptions. In this article, MCF was validated for point connections and in conditions where SEA assumptions are not met (systems with low modal overlap, non-conservative junctions, strong coupling). The effect of removing MCF bias on the results was also examined. During the experiments, it was observed that the bias is inversely proportional to the damping loss factor of the examined subsystems. The obtained results confirm that the PIM, combined with MCF, allows to determine non-negative SEA parameters in all considered cases.

2

Quality assessment of speech signals under a process of echo cancelation in telecommunications systems

Dobrucki Andrzej, Kin Maurycy, Walczyński Maciej

Vibrations in Physical Systems

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2022

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Vol. 33, nr 1

art. no. 2022111

EN

The phenomenon of echo in the telecommunications channels is caused by the reflection of an electrical signal in a long line. In order to improve the quality of the transmitted sound, various adaptive filters are used to remove or at least reduce the level of the reflected delayed signal. However, such a process may result in a degradation in the quality of speech, although its intelligibility may not get worse. The work presents the results of subjective studies on assessing the quality of speech signals under the process of acoustic echo cancellation using different algorithms. The algorithms studied were: LMS (Least Mean Squares), NLMS (Normalized Least Mean Squares) and AP (Affine Projection). The study consisted of assessing the signal quality after applying the echo elimination process using the Degradation Category Rating method. A total of 312 signals were used in the test: 192 male speech and 120 female speech samples. Echo simulation was used using different delay times and levels of echo signal. Both types of speech have signal delay times of 20 ms, 50 ms, 100 ms and 200 ms with echo level values of -6 dB, -12 dB, -18 dB and -24 dB. In addition, for female speech signals, a delay time of 150 ms was introduced. The study involved 14 people aged between 18 and 38, including six women and eight men. All subjects had normal good hearing. Seven listeners had participated in subjective listening tests of the sound quality assessment previously. The listeners’ opinions were collected on prepared questionnaire. It was found that the highest ratings were given to the AP filter, while the worst ratings were featured the NLMS. It should also be noted that the range between the results obtained for AP and NLMS for female speech is smaller in comparison to male. It is also interesting that the discrepancy in ratings was greatest for a delay time of 100 ms for the AP filter and 200 ms for the LMS filter. It can therefore be concluded from the obtained results that, in the case of acoustic echo cancelation, AP filter introduced the lowest quality degradation while the LMS achieved slightly worse average ratings when compared to the AP filter . The NLMS filter characterized by the worst ratings, and in some cases received twice the quality degradation compared to the AP filter.

3

Impact of the level of noise and echo on the reaction time of listeners in the perception of logatoms

Brachmański Stefan, Dobrucki Andrzej

Vibrations in Physical Systems

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2021

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Vol. 32, nr 2

art. no. 2021215

EN

The article presents the results of research regarding the impact of the degree of distortion and noise of the logatom (nonsense word) on the listener's reaction time. The study aimed to determine the maximum reaction time of listeners, which will allow determining the time after which the logatom will be exposed in the speech quality assessment method with an alternative choice. The research was carried out with the participation of a group of ten students. A strong relationship between the results obtained and the concentration of the listeners was found, as well as the effect of fatigue, training, and the gender of the listener. The obtained results indicate that in the method with an alternative choice before the logatom emission should appear 1.1 s initial sequence, which will eliminate the situation when the listeners did not recognize the initial phoneme transmitted from the logatom.

4

Active Cancellation of the Tonal Component of Sound Using a Discrete Fourier Transform of Variable Length

Łuczyński Michał, Dobrucki Andrzej, Brachmański Stefan

Archives of Acoustics

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2021

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Vol. 46, No. 4

579--589

EN

The paper presents a method of eliminating the tonal component of an acoustic signal. The tonal component is approximated by a sinusoidal signal of a given amplitude and frequency. As the parameters of this component: amplitude, frequency and initial phase may be variable, it is important to detect these parameters in subsequent analysis time intervals (frames). If the detection of the parameters is correct, the elimination consists in adding a sinusoidal component with the detected amplitude and frequency to the signal, but the phase shifted by 180 degrees. The accuracy of the reduction depends on the accuracy of parameters detection and their changes. Detection takes place using the Discrete Fourier Transform, whose length is changed to match the spectrum resolution to the signal frequency. The operation for various methods of synthesis of the compensating signal as well as various window functions were checked. An elimination simulation was performed to analyze the effectiveness of the reduction. The result of the paper is the assessment of the method in narrowband active noise control systems. The method was tested by simulation and then experimentally with real acoustic signals. The level of reduction was from 6.9 to 31.5 dB.

5

Jakość sygnału mowy emitowanego w lokalnej radiofonii cyfrowej w wybranych punktach Wrocławia

Brachmański Stefan, Dobrucki Andrzej, Rurzyńska Natalia, Zemankiewicz Patrycja

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

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2020

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nr 7-8

324--327, CD

PL

W październiku 2018 roku została uruchomiona lokalna radiofonia cyfrowa pokrywająca swoim zasięgiem aglomerację Wrocławia. Realizacja tego przedsięwzięcia wymagała wykonania wielu testów, w tym również jakościowych odnoszących się zarówno do muzyki jak i mowy. W niniejszym artykule przedstawiono wyniki testów jakościowych opartych na ocenie jakości mowy sygnałów nagranych w różnych punktach Wrocławia. Pomiary wykonano zgodnie z zaleceniami International Telecommunication Union. Ocena została wykonana dla głosu męskiego i żeńskiego.

EN

In October 2018, local digital radio was launched to cover the agglomeration of Wrocław. The implementation of this undertaking required many tests, including qualitative ones, referring to both music and speech. This article presents the results of qualitative tests based on evaluation of speech quality of signals recorded at various points in Wrocław. The measurements were carried out in accordance with the recommendations of the International Telecommunication Union. The rating was made for male and female voice.

6

Influence of Working Conditions on Parameters of Thermoacoustic Engine with Travelling Wave

Dobrucki Andrzej, Kruk Bartłomiej

Archives of Acoustics

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2020

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Vol. 45, No. 3

467--473

EN

Thermoacoustic converters are devices for direct conversion of acoustic energy into thermal energy in the form of temperature difference, or vice versa – for converting thermal energy into an acoustic wave. In the first case, the device is called a thermoacoustic heat pump, in the second – thermoacoustic engine. Thermoacoustic devices can use (or produce) a standing or travelling acoustic wave. This paper describes the construction and properties of a single-stage thermoacoustic engine with a travelling wave. This kind of engine works using the Stirling cycle. It uses gas as a working medium and does not contain any moving parts. The main component of the engine is a regenerator equipped with two heat exchangers. Most commonly, a porous material or a set of metal grids is used as a regenerator. An acoustic wave is created as a result of the temperature difference between a cold and a hot heat exchanger. The influence of working gas, and such parameters as static pressure and temperature at heat exchanger on the thermoacoustic properties of the engine, primarily its efficiency, was investigated. The achieved efficiency was up to 1.4% for air as the working medium, which coincides with the values obtained in other laboratories. The efficiency for argon as working gas is equal to 0.9%.

7

Objective and subjective evaluation of musical and speech recordings transmitted by DAB+ system

Dobrucki Andrzej, Brachmański Stefan, Kin Maurycy

Vibrations in Physical Systems

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2019

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Vol. 30, nr 1

art. no. 2019104

EN

The results of research on the sound quality of various kinds of music as well as speech signals transmitted via Digital Audio Broadcasting Plus system are presented. The results showed that bitrate values significantly influence the results of quality assessment, i.e. the overall audio quality as well as a timbre are dependent on the bitrate. The additional conclusion is that the CCR method is more accurate for sound assessment for higher bitrate values and this fact has been verified by standard deviation values of obtained results. The speech signals were additionally examined with PESQ method. The results have shown that the assumed quality of 4 MOS for speech could be achieved at 48 kbps. This fact was confirmed by both: subjective and objective research.

8

Transmisja głosowych komunikatów drogowych w radiofonii cyfrowej DAB+

Falkowski-Gilski Przemysław, Brachmański Stefan, Dobrucki Andrzej

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

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2019

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nr 6

334--337, CD

PL

Proces cyfryzacji radia jest nowym rozdziałem w historii radiofonii. Wiele rekomendacji i badań naukowych wskazuje na standard DAB+ (Digital Audio Broadcasting plus), który w niedalekiej przyszłości ma zastąpić analogową radiofonię FM. Ten system cyfrowy wprowadza wiele zmian, oferując przy tym lepszą jakość dźwięku oraz szereg usług dodatkowych. W pracy postanowiono zbadać minimalną wymaganą przepływność bitową potrzebną do transmisji głosowych komunikatów drogowych w ramach radiofonii cyfrowej DAB+.

EN

The process of digitizing radio marks a new chapter in the history of broadcasting. Numerous recommendations and scientific publications point out to DAB+ (Digital Audio Broadcasting plus), as the standard that will replace traditional analog FM radio in the nearest future. This digital system implies changes, offering higher sound quality, as well as a set of additional services. In this work we present a study concerning minimal required bitrate necessary for transmitting voice traffic messages in the DAB+ broadcasting system.