HIS 140 - Amplification and Residual Hearing Ability

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HIS 140 - Amplification and Residual Hearing Ability

  1. 1. Amplification & Residual Hearing Ability  Historic review Horns and acoustic devices only improved the efficiency of the hearing system—they did not increase the power to the hearing system.
  2. 2. Amplification & Residual Hearing Ability  Historic Review Four items began the evolution into modern electronic hearing instruments. They were:1. The transistor2. The integrated chip3. Button cell battery improvements4. Miniature—high quality transducers
  3. 3. Amplification & Residual Hearing Ability  Historic Review In 1971, the Federal Trade Commission issued a ruling that no hearing company could claim that the use of two hearing aids would provide the consumer with any benefit greater that the use of one hearing aid.
  4. 4. Amplification & Residual Hearing Ability  Amplification Review We have covered the various classes of analog amplifiers.1. Class A2. Class B3. Class D4. Class H
  5. 5. Amplification & Residual Hearing Ability  Amplification Review All electronic amplifiers produce harmonic overtones and distortion not present in the input signal. This is termed intermodulation distortion.
  6. 6. Amplification & Residual Hearing Ability  Amplification Review When the complex sound of speech is input into the amplifier, summations and differences (additional frequencies created due to the nature of amplified frequencies) of both low and high frequency information may also result.
  7. 7. Amplification & Residual Hearing Ability  Digital Amplification It has a great advantage over analog amplification because it can perform very efficiently in large noise environments. Computer/digital adjustments to this type of amplifier have now also become very discreet and refined.
  8. 8. Amplification & Residual Hearing Ability  Digital Amplification While it has created a better opportunity to operate in noise in environments, it does not have the ability to differentiate speech from noise. Again, one person’s “music” is another person’s noise.
  9. 9. Amplification & Residual Hearing Ability  Digital Amplification It certainly provides much more discreet shaping of frequencies and compression applications i.e. signal processing.
  10. 10. Amplification & Residual Hearing Ability  Signal Processing With conductive hearing loss, frequency response shaping is normally all that is required. With cochlear impairment, both frequency response shaping and compression are required due to the recruitment characteristics of cochlear outer hair cell damage.
  11. 11. Amplification & Residual Hearing Ability  Signal Processing Improving speech intelligibility with cochlear damage requires that the residual dynamic range of the patient/client be identified and appropriate amplification applied.
  12. 12. Amplification & Residual Hearing Ability  Signal Processing Three kinds of signal treatment are necessary to address this type of hearing impairment. They are:1. Amplification that compensates for the increase of hearing loss for weak signals.2. Amplification that simultaneously compensates for the increase of hearing loss by frequency.3. Signal processing which places the amplified signal into the patient/client’s residual dynamic range.
  13. 13. Amplification & Residual Hearing Ability  Signal Processing Amplification analogous with eyewear is described in Villchur page #92. Let’s review this analogy and discuss.
  14. 14. Amplification & Residual Hearing Ability  Residual Hearing Ability The dynamic range of audible speech must be introduced into the reduced dynamic range of cochlear hearing loss. Let’s review Villchur pg#93, 95, 99, & 101
  15. 15. Amplification & Residual Hearing Ability  Signal Processing & Residual Ability Skinner found that when greater intensity high frequencies are introduced; the less the high frequency emphasis became effective or tolerated by the patient/client.
  16. 16. Amplification & Residual Hearing Ability  Compression & Residual Hearing Ability Compression strategies used for cochlear damage are:1. Wide dynamic range compression2. Compression limiting3. Frequency compression
  17. 17. Amplification & Residual Hearing Ability  Compression & Residual Hearing Ability The compression strategies use frequency shaping, attack and release times, and compression ratios to accomplish the task of placing sound information into the residual dynamic range.
  18. 18. Amplification & Residual Hearing Ability  Compression & Residual Hearing Ability A typical patient/client has recruitment and requires far less gain at speech levels than at threshold levels The goal of a compression system is not to reduce the levels of high intensity sounds; but, to amplify high intensity signals to the their optimum level and to increase the relative gain of low intensity signals as it corresponds to the patient/client’s residual hearing ability.
  19. 19. Amplification & Residual Hearing Ability  Compression & Recruitment Recruitment is a deficiency in the normal compressing action of the outer hair cells which modifies the entire dynamic range of speech and music to be accepted by the inner hair cells. Let’s review this phenomena as illustrated in Villchur pg #104.
  20. 20. Amplification & Residual Hearing Ability  Compression & Recruitment It is well known that the combination of recruitment and high frequency hearing loss significantly erodes speech intelligibility. Digital hearing instrument processing is intended to create maximum use of the damaged cochlea it will not regain/restore the performance of a damaged cochlea.
  21. 21. Amplification & Residual Hearing Ability  Future Signal Processing Signal processing for profound hearing loss is moving into the world is cochlear implant improvements.
  22. 22. Amplification & Residual Hearing Ability  Future Signal Processing Hearing impaired listeners will always be challenged with the ability to hear in noise. There are microphone configurations which assist with this necessity. To date, there are no digital algorithms proven to support this requirement of an amplifier.

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