Proceedings Fonetik 2009 - Institutionen för lingvistik

Proceedings, FONETIK 2009, Dept. of Linguistics, Stockholm Universityfor hearing impaired people with different hearingloss levels. The tests investigate how muchsubjects benefit from the use of SynFace interms of speech intelligibility, and how difficultit is for a subject to understand speech with thehelp of SynFace. Following is a detailed descriptionof methods used in these tests.MethodSRT or Speech Reception Threshold is thespeech signal SNR when the listener is able tounderstand 50% of the words in the sentences.In this test, SRT value is measured one timewith a speech signal alone without SynFace,with two types of noise, and another time withthe use of (when looking at) SynFace. If theSRT level has decreased when using SynFace,that means the subject has benefited from theuse of SynFace, since the subject could understand50% of the words with a higher noiselevel than when listening to the audio signalalone.To calculate the SRT level, a recursive proceduredescribed by Hagerman & Kinnefors(1995), is used, where the subject listens tosuccessive sentences of 5 words, and dependingon how many words the subject recognizes correctly,the SNR level of the signal is changed sothe subject can only understand 50% of thewords.The SRT value is estimated for each subjectin five conditions, a first estimation is used astraining, to eliminate any training effect. Thiswas recommended in Hagerman, B., & Kinnefors(1995). Two SRT values are estimated inthe condition of speech signal without SynFace,but with two types of noise, Stationary noise,and Babble noise (containing 6 speakers). Theother two estimations are for the same types ofnoise, but with the use of SynFace, that is whenthe subject is looking at the screen with Syn-Face, and listening in the head-phones to a noisysignal.In the effort scaling test, the easiness of usingSynFace by hearing impaired persons wastargeted.To establish this, the subject has to listen tosentences in the headphones, sometimes whenlooking at SynFace and sometimes withoutlooking at SynFace, and choose a value on apseudo continuous scale, ranging from 1 to 6,telling how difficult it is to listen to the speechsignal transmitted through the head-phones.Small Scale SRT Study on Normal HearingsubjectsA first small scale SRT intelligibility experimentwas performed on normal hearing subjectsranging in age between 26 and 40. Thisexperiment is established in order to confirmthe improvement in speech intelligibility of thecurrent SynFace using the SRT test.The tests were carried out using five normalhearing subjects. The stimuli consisted of twoSRT measurements while each measurementused a list of 10 sentences, and stationary noisewas added to the speech signal. A training sessionwas performed before the real test to controlthe learning effect, and two SRT measurementswere performed after that, one withoutlooking at SynFace and one looking at Syn-Face. Figure 1 shows the SRT levels obtainedin the different conditions, where each line correspondsto a subject.It is clear in the figure that all 5 subjects requiredlower SNR level when using SynFacecompared to the audio-only condition and theSRT for all of them decreased in the audio+SynFacecondition.An ANOVA analysis and successive multiplecomparison analysis confirm that there is asignificant decrease (improvement) of SRT (p