Adaptiiviset läpikuuluvuuskuulokkeet

Hear-through equalization can be used to make a headset acoustically transparent, i.e.~to produce sound perception that is similar to perception without the headset. The headset must have microphones outside the earpieces to capture the ambient sounds, which is then reproduced with the headset transducers after the equalization. The reproduced signal is called the hear-through signal. Equalization is needed, since the headset affects the acoustics of the outer ear. \\ In addition to the external microphones, the headset used in this study has additional internal microphones. Together these microphones can be used to estimate the attenuation of the headset online and to detect poor fit. Since the poor fit causes leaks and decreased attenuation, the combined effect of the leaked sound and the hear-through signal changes, when compared to proper fit situation. Therefore, the isolation estimate is used to control the hear-through equalization in order to produce better acoustical transparency. Furthermore, the proposed adaptive hear-through algorithm includes manual controls for the equalizers and the volume of the hear-through signal. \\ The proposed algorithm is found to transform the used headset acoustically transparent. The equalization controls improve the performance of the headset, when the fit is poor or when the volume of the hear-through signal is adjusted, by reducing the comb-filtering effect due to the summation of the leaked sound and the hear-through signal inside the ear canal. The behavior of the proposed algorithm can be demonstrated with an implemented Matlab simulator.Läpikuuluvuusekvalisoinnilla voidaan saavuttaa akustinen läpinäkyvyys kuulokkeita käytettäessä, eli tuottaa samankaltainen ääniaistimus kuin mikä havaittaisiin ilman kuulokkeita. Käytetyissä kuulokkeissa tulee olla mikrofonit kuulokkeen ulkopinnalla, joiden avulla voidaan tallentaa ympäröiviä ääniä. Mikrofonisignaalit ekvalisoidaan, jolloin niistä tulee läpikuuluvuussignaalit, ja toistetaan kuulokkeista. Ekvalisointi on tarpeellista, sillä kuulokkeet muuttavat ulkokorvan akustiikka ja siten myös äänihavaintoa. \\ Tässä diplomityössä käytetyssä prototyyppikuulokeparissa on edellä mainittujen mikrofonien lisäksi myös toiset, korvakäytävän sisälle asettuvat mikrofonit. Yhdessä näiden kahden mikrofonin avulla voidaan määrittää reaaliaikainen estimaatti kuulokkeen vaimennukselle ja tunnistaa huono istuvuus. Koska huonosti asetettu kuuloke vuotaa enemmän ääntä korvakäytävän sisään kuin kunnolla asetettu, kuulokkeen äänen ja vuotavan äänen yhteisvaikutus muuttuu. Tästä syystä vaimennusestimaattia käytetään läpikuuluvuusekvalisoinnin säätöön, jotta akustinen läpinäkyvyys ei kärsisi. Lisäksi esitellyssä algoritmissa on manuaaliset säädöt ekvalisaattoreille ja läpikuuluvuussignaalin voimakkuudelle.\\ Esitetyn algoritmin havaitaan tuottavan akustinen läpinäkyvyys, kun sitä käytetään prototyyppikuulokkeiden kanssa. Ekvalisointisäädöt parantavat kuulokkeiden toimintaa istuvuuden ollessa huono tai säädettäessä läpikuuluvuussignaalin voimakkuutta, koska ne vähentävät kampasuodatusefektiä, joka voi aiheutua vuotavan äänen ja läpikuuluvuussignaalin summautuessa. Esitellyn algoritmin toimintaa voidaan havainnollistaa toteutetulla Matlab-simulaattorilla

On the audibility of all-pass phase in electroacoustical transfer functions

Audible effects of second-order all-pass sections with center frequencies in the range of 1-12 kHz were studied in headphone listening experiments. All-pass sections give rise to two effects. 1) A perception of "ringing" or "pitchiness," which is related to an exponentially decaying sinusoid in the impulse response of all-pass sections with high Q factors. The ringing is especially audible for impulsive sounds, whereas it is often masked with everyday sounds such as speech and music. With an impulse signal the ringing was found to be audible when the decay time constant for the sinusoid exceeds approximately 0.8 ms (peak group delay of 1.6 ms), independent of the center frequency within the frequency range studied. 2) A lateral shift of the auditory image, which occurs when an all-pass section is inserted in the signal path to only one ear. The shift is related to the low-frequency phase and group delays of the all-pass section, and it was found to be audible whenever t hese exceed approximately 35 s, independent of the signal

The active control of low frequency room modes

The normal modes of an enclosed sound field introduce spatial, time and frequency domainartefacts to signals reproduced in such an environment, such that undesirable colourationof these signals may be perceived. Modal density with respect to frequency is minimal atlow frequencies, and in small rooms this means that widely spaced discrete modes dominatesound reproduction up to frequencies of the order of one hundred Hertz. The removal ofunwanted colouration is not straightforward; conventional passive absorptive treatmentsoffer poor performance at low frequencies, and where their use is attempted costs (in termsof space consumption) may be prohibitive.This Thesis presents a series of investigations into the active control of low frequencyacoustic resonance, using both adaptive digital filters in feedforward and feedbackconfigurations, and fixed feedforward controllers. The adaptive filters are based around theactive control of acoustic impedance, using hardware available to the project as the productof previous work at Salford University. The application of the technique to the control ofmodes in a three dimensional environment is however novel. The fixed feedforwardcontrollers use a novel application of an analytical modal decomposition of an enclosedsoundfield as the basis for a digital IIR acoustic model. This model is utilised in order tomanipulate the locations of z-plane poles and change the behaviour of the sound field.These two techniques are applied to a number of control tasks in one- and threedimensionaltest environments, using numerical models and practical hardwareimplementations. The tasks include pressure cancellation, and more usefully the control offrequency domain Q-factor and corresponding modal decay times. It is shown that activeimpedance methods are superior in the duct; the fixed feedforward controllers suffer fromthe combined effect of the finite source impedance of practical control loudspeakers withchanging and strongly modal radiation loads. In the room, both techniques are shown to becapable of useful reductions in modal Q-factor and decay time. Fixed methods offer controlover a defined spatial volume, and adaptive techniques may be further developed by therefinement of the control hardware

Proceedings of the 19th Sound and Music Computing Conference

Proceedings of the 19th Sound and Music Computing Conference - June 5-12, 2022 - Saint-Étienne (France). https://smc22.grame.f

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion