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Improving audibility as a foundation for better speech understanding Pamela Souza, PhD Northwestern University Evanston, IL.

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Presentation on theme: "Improving audibility as a foundation for better speech understanding Pamela Souza, PhD Northwestern University Evanston, IL."— Presentation transcript:

1 Improving audibility as a foundation for better speech understanding Pamela Souza, PhD Northwestern University Evanston, IL

2 Outline O The talker: producing clear speech O The listener: effects of hearing loss O Speech audibility O Distance, noise and echoes O Improving audibility: hearing aids and cochlear implants

3 Communication: “send and receive”

4 Speech varies rapidly in time, frequency (pitch), and intensity (loudness)

5 Speech is redundant – we don’t need to hear every sound. But the more information is received, the less effort is needed to listen High redundancy: quiet, visual cues, high context Low redundancy: noisy, no visual cues, low context

6 Severe Audibility is determined by the level of the speech, the level of any noise, and the listener’s audiogram Sensitive hearing Mild Moderate

7 Understanding the audiogram Amount of hearing lossRehabilitation choices MildMay use hearing aid if communication is affected ModeratePartial audibility of conversational speech; hearing aid recommended Moderately severePoor audibility of conversational speech; hearing aid recommended SevereInaudibility of conversational speech; hearing aid, cochlear implant, or alternative communication mode Profound

8 Soft speech, no hearing aid, 29% audible Loud speech, no hearing aid, 57% audible Pink line shows upside-down audiogram (high-frequency loss) Louder Audibility is higher when the talker’s voice is louder (or closer)

9 Effects of distance and position The further the talker is from the listener, the lower audibility will be

10 Effects of background noise

11 O Energetic masking: reduces audibility when noise overlaps in pitch and timing with the speech, blocking the speech from being heard O Informational masking: when noise does not overlap with speech energy, but causes confusion or draws attention away from the talker O More effort is required to listen in noise

12 Effects of reverberation (echoes)

13 Effects of reverberation O Sound reaches the listener directly O A delayed version of the same sound reaches the listener after reflecting from a hard surface O Overlap masking: the delayed sound is still present and energetically masks sounds that follow O More effort is required to listen in reverberation

14 Improving audibility O Improving signal O Reducing distance O Eliminating noise and reverberation O Hearing aids and cochlear implants O Assistive listening devices with remote microphones

15 What does the hearing aid do to improve audibility? O Customized frequency-gain response O Multichannel compression O Frequency lowering O Noise reduction O Suppressing reverberation (echoes)

16 Frequency-gain response O Provides more amplification (“gain”) at frequencies where there is more hearing loss O Like a mirror of the audiogram O Different mathematical formulas or “prescriptions” (such as DSL and NAL) are used to determine desired response

17 Improving audibility: frequency-gain response Audiogram shows high- frequency hearing loss Hearing aid gain should be greater in high frequencies Speech audibility is improved in high frequencies

18 Soft speech 29% audible Loud speech 57% audible Without hearing aidWith linear hearing aid Soft speech 51% audible Loud speech 79% audible Louder Too loud Linear aids improve audibility, but may cause loudness discomfort

19 Multichannel compression O Within each frequency band, soft sounds are amplified more than loud sounds O Reduces the dynamic range from soft to loud O Soft sounds should be made more audible without making loud sounds too loud O But –more extreme compression parameters may distort speech

20 Soft speech 29% audible Loud speech 57% audible Without hearing aidWith compression hearing aid Louder Soft speech 59% audible Loud speech 79% audible Compression hearing aids improve audibility and loudness comfort (without volume adjustments)

21 Audible bandwidth and frequency lowering amplification O Listeners with sensitive hearing receive sounds to 8000 Hz or higher; most listeners wearing hearing aids receive sounds up to Hz O A wider bandwidth may improve speech understanding O A wider bandwidth may make it easier for children to learn new information O A wider bandwidth supports speech production Gustafson & Pittman, 2011; Pittman, 2008; Stelmachowicz et al., 2004;

22 Frequency lowering hearing aids O Used to improve high-frequency sound audibility O High-frequency sounds are shifted to a lower frequency range O May be more beneficial for children than adults (due to adults’ greater linguistic experience) O Should be used selectively (more studies are in progress) Souza et al. 2013; McCreery et al., 2014; Bentler et al., 2014

23 Hearing aid noise reduction: directional microphones O Apply less gain to noise that is from a different location than the talker O Improve the relative levels of the talker (“signal”) and the background (“noise”) O Can improve speech audibility (and understanding) if signal and noise are spatially separated

24 Hearing aid noise reduction: digital noise reduction O Attempts to determine what is “noise” and what is “speech” based on their sound patterns O Mathematically removes the pattern of the noise O May not improve speech understanding, but can reduce listening effort and improve listening comfort

25 Assistive listening devices O Overcome distance by placing the microphone close to the talker’s lips and transmitting that signal to the listener’s hearing aid O Suppress noise and reverberation by transmitting the “clean” signal direct from the talker O Can be used anywhere distance or noise is an issue: classroom, automobile, restaurant

26 How much audibility is enough? O When background noise limits audible speech, adult listeners with sensitive hearing need about 50% audibility to understand 80% of sentences Results from Souza, Boike, Witherell, Tremblay, 2007 Adults with sensitive hearing are similar to each other – if speech is at least 60% audible, it is usually understood

27 How much audibility is enough? O When background noise limits audible speech, adult listeners with hearing loss need about 80% audibility to understand 80% of sentences Results from Souza, Boike, Witherell, Tremblay, 2007 With hearing loss, good audibility does not always mean good speech understanding

28 Children need greater audibility than adults McCreery & Stelmachowicz, 2011 Better understanding Better audibility Adults Age 5-8 years Age 9-12 years When children and adults are getting the same amount of audible information, children have more difficulty understanding speech than adults do

29 Audibility for children O Child-centric hearing aid fitting procedures emphasize audibility O Child audibility needs are assumed to be different from adults O Audibility may be addressed differently by pediatric audiologists than by adult audiologists

30 Using cognitive ability to “fill in” inaudible information O We unconsciously use memory and knowledge to extract meaningful information from a partially audible signal O Adults are good at using context; children have more difficulty (due to limited linguistic experience) O This process uses cognitive resources

31 Summary O Talkers should be close to the listener, visible, and producing clear speech O Reduce background noise! O Hearing aids (with appropriate settings and features) O Assistive listening devices for more difficult (noisy or distant) situations O Conversation is a two-part experience

32 Thank you contact: Research web site: halab.northwestern.edu


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