Techniques for speech intelligibility enhancement in mobile telephony
Emma Jokinen · 2017
Today's consumers can use their mobile telephony devices almost anywhere and at any time. This means that speech communication is often disturbed by environmental background noise, making it hard for the listener to understand what the speaker is saying. To further aggravate the situation, the listener and the speaker are typically in different locations when the communication is taking place. This means that without listener feedback the speaker is unable to adjust his or her speaking style to fit the listening environment, as is normally done in face-to-face communication situations. However, speech communication by mobile telephony in noisy conditions can be improved using intelligibility enhancement technology. This thesis contributes to the development of intelligibility enhancement techniques that can in principle be applied in real-time speech communication in a mobile device. The algorithms are intended to be used in a post-processing block in the receiving device to combat near-end noise in the listener's environment. The target application places tight restrictions on the algorithmic delay, which means that frame-based processing in short time frames (for instance, 10 to 20 ms in length) must be employed. Several algorithms for intelligibility improvement are proposed and their performance is demonstrated with subjective tests using simulated telephone speech. The majority of the introduced algorithms aim to mimic modifications that human speakers naturally employ when talking in noisy situations. In addition, a feature extraction technique that can be used to estimate the spectral tilt caused by the glottal excitation from telephone speech is proposed. Finally, the impact of noisy far-end conditions on post-processing in the receiving device is investigated. In general, the proposed post-processing techniques show clear intelligibility improvement over unprocessed telephone speech, ranging up to a 40 percentage point reduction in word-error rates.; Kuluttajat voivat nykypaivana kayttaa mobiililaitteitaan lahes missa ja milloin vain. Tama tarkoittaa puolestaan sita, etta ymparistossa oleva melu hairitsee kuuntelijaa tehden puhujan viestin ymmartamisesta haastavampaa. Tilannetta vaikeuttaa entisestaan se, etta puhuja ja kuuntelija ovat usein fyysisesti eri paikoissa puhuessaan keskenaan. Talloin puhuja ei valttamatta aina pysty mukauttamaan puhetyyliaan kuuntelijan ympariston mukaan, kuten normaalisti tapahtuisi kasvokkain kaytavassa keskustelussa. Mobiililaitteissa tapahtuvan kommunikaation sujuvuutta meluisissa tilanteissa voidaan kuitenkin lisata ymmarrettavyyden parantamiseen tahtaavilla tekniikoilla. Tassa vaitoskirjassa on kehitetty puheen ymmarrettavyyden parantamiseen kaytettavia algoritmeja, jotka periaatteessa soveltuvat reaaliaikaiseen kommunikaatioon mobiililaitteissa. Nama algoritmit on tarkoitettu erityisesti puheen jalkikasittelyyn vastaanottavassa laitteessa ja niiden tavoitteena on kuuntelijan ymparilla olevan taustamelun vaikutusten vahentaminen. Reaaliaikaisuus vaatimuksena tarkoittaa,…