his 140 - amplification and residual hearing ability

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.


Historic Review

Four items began the evolution into modern electronic hearing instruments. They were:

1. The transistor

2. The integrated chip

3. Button cell battery improvements

4. Miniature—high quality transducers


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.


Amplification Review

We have covered the various classes of analog amplifiers.

1. Class A

2. Class B

3. Class D

4. Class H



All electronic amplifiers produce harmonic overtones and distortion not present in the input signal. This is termed intermodulation distortion.



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.


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.



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.



It certainly provides much more discreet shaping of frequencies and compression applications i.e. signal processing.


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.


Signal Processing

Improving speech intelligibility with cochlear damage requires that the residual dynamic range of the patient/client be identified and appropriate amplification applied.


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.


Signal Processing

Amplification analogous with eyewear is described in Villchur page #92.

Let’s review this analogy and discuss.


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


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.


Compression & Residual Hearing Ability

Compression strategies used for cochlear damage are:

1. Wide dynamic range compression

2. Compression limiting

3. Frequency compression



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.



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.


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.


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.


Future Signal Processing

Signal processing for profound hearing loss is moving into the world is cochlear implant improvements.


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.

his 140 - amplification and residual hearing ability

Technology

hearing systemthey

hearing aids

hearing company

analog amplification

appropriate amplification

increase of hearing

conductive hearing loss

type of hearing impairment