Spherical Microphone Array Processing for Acoustic Parameter Estimation and Signal Enhancement by Daniel P. Jarrett ) s t e b a H l ë u n a m E dit: e r c o ot h P ( y. a r r a e n o h p o r c mi Athesissubmittedinfulfilmentofrequirementsforthedegreeof al c DoctorofPhilosophyofImperialCollegeLondon eri h p s Communications&SignalProcessingGroup ke mi DepartmentofElectrical&ElectronicEngineering n e ImperialCollegeLondon Eig 2013 The n: o ati r t s u Ill 3 Copyright declaration ThecopyrightofthisthesisrestswiththeauthorandismadeavailableunderaCreative CommonsAttributionNon-CommercialNoDerivatives licence. Researchersarefreeto copy,distributeortransmitthethesisontheconditionthattheyattributeit,thattheydo notuseitforcommercialpurposesandthattheydonotalter,transformorbuilduponit. Foranyreuseorredistribution,researchersmustmakecleartoothersthelicenceterms ofthiswork. 5 Statement of originality Ideclarethatthisthesisandtheresearchtowhichitrefersaretheproductofmyown workundertheguidanceandsupervisionofDrEmanuëlA.P.Habetsandmythesis supervisorDrPatrickA.Naylor. Anyideasorquotationsfromtheworkofothers, publishedorotherwise,arefullyacknowledgedinaccordancewithstandardreferencing practice. Thematerialofthisthesishasnotbeenacceptedforanydegree,andhasnot beenconcurrentlysubmittedfortheawardofanyotherdegree. 7 Abstract Inmanydistantspeechacquisitionscenarios,suchashands-freetelephonyorteleconfer- encing,thedesiredspeechsignaliscorruptedbynoiseandreverberation. Thisdegrades boththespeechqualityandintelligibility,makingcommunicationdifficultorevenim- possible. Speechenhancementtechniquesseektomitigatetheseeffectsandextractthe desiredspeechsignal. Thisobjectiveiscommonlyachievedthroughtheuseofmicrophonearrays,which takeadvantageofthespatialpropertiesofthesoundfieldinordertoreducenoiseand reverberation. Sphericalmicrophonearrays,wherethemicrophonesarearrangedina sphericalconfiguration,usuallymountedonarigidbaffle,areabletoanalyzethesound fieldinthreedimensions;thecapturedsoundfieldcanthenbeefficientlydescribedin thesphericalharmonicdomain(SHD). Inthisthesis,anumberofnovelsphericalarrayprocessingalgorithmsareproposed, basedintheSHD.Inordertocomprehensivelyevaluatethesealgorithmsunderavariety of conditions, a method is developed for simulating the acoustic impulse responses betweenasoundsourceandmicrophonespositionedonarigidsphericalarrayplaced inareverberantenvironment. Theperformanceofspeechenhancementalgorithmscanoftenbeimprovedbytaking advantageofadditionalaprioriinformation,obtainedbyestimatingvariousacoustic parameters. Methodsforestimatingtwosuchparameters,thedirectionofarrival(DOA) ofasource(staticormoving)andthesignal-to-diffuseenergyratio,areintroduced. 8 Abstract Finally,thesignalsreceivedbyamicrophonearraycanbefilteredandsummedby abeamformer. Atradeoffbeamformerisproposed,whichachievesabalancebetween speechdistortionandnoisereduction. Thebeamformerweightsdependonthenoise statistics,whichcannotbedirectlyobservedandmustbeestimated. Anestimationalgo- rithmisdevelopedforthispurpose,exploitingtheDOAestimatespreviouslyobtained todifferentiatebetweendesiredandinterferingcoherentsources. 9 Acknowledgements Firstandforemost,Iwouldliketothankmysupervisor,PatrickNaylor,forencour- agingmetoundertakethisPhD.Inaddition,Iamthankfulforhissupport,guidance andoptimismthroughoutmytimeasaPhDstudent. Iwouldalsoliketoexpressmy appreciationtoEmanuëlHabetsforhissupervision,adviceandrelentlessattentionto detail,aswellashiswillingnesstogivehistimesogenerously. DuringmyPhDIspent fourmonthsatInternationalAudioLaboratoriesErlangen,andIamgratefultoEmanuël forthisopportunity. IthankmyfriendsandcollaboratorsMarkThomasandNikolay Gaubitchfortheirhelpwithmyresearch. Inaddition,IwouldliketothankmyfriendsandcolleaguesintheCommunications &SignalProcessing group,including Felicia,James,Jason,Marco,SiraandZiggy, andmyfriendsoutsidetheoffice,inparticularBenoît,Letizia,Lise,Marine,Nicolas, Pietro, Quentin and Sophie, for making my time as a PhD student more fun and keepingmyspiritshigh. Iwouldliketooffermyspecialthankstomyparentsandsister forenduringthisprocesswithme,andfortheirloveandmoralsupport. Finally, I would like to acknowledge the financial support of the Engineering and PhysicalSciencesResearchCouncil(EPSRC)intheformofaDoctoralTrainingGrant. DanielJarrett