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1. Boystown article on the “Benefits of Digital Hearing Aids”. 2. ASHA article by Ricketts on Digital Hearing Aids “State of the Art”. 3. Define and discuss the various levels of hearing aid circuitry / technology that have been available through the years. 4. Discuss the goals of successful amplification. a. ACT b. A udible, C omfortable, T olerable 5. Define and discuss each of the basic components of all hearing aids. a. All hearing aids have i. Microphone -picks up acoustic signals in the environment and converts them to an electrical signal which goes to a series of amplifiers 1. Directional (responds most effectively to sounds originating in front)/ Omnidirectional (responds equally to sounds regardless of their azimuth) ii. Amplifier - electronic circuit that amplify, shape, and limit the electrical signal from the microphone 1. Analog or digital 2. Can be manually set or programmed iii. Battery - All HA’s use a batter to power the aid 1. 1.3-1.5 volts, AA, Zinc Air iv. Receiver -Mini loudspeaker that converts the electrical output from the amps or signal processing circuit to an acoustic singal 1. Internal (Receiver built into HA) /External (Receiver is external, connected to a HA via a wire) 6. Define and discuss the various controls or features that may be found on hearing aids. a. External User Controls: i. On/off switch (O-FS) ii. M-O-T- or MT Switch 1. M- Ha microphone turned on, O- HA microphone turned off, T- telecoil is turned off, M/T- both microphone and telecoil are turned on iii. Telecoil , T-switch - special circuit that picks up electromagnetic energy from a telephone receiver or other device that radiates electromagnetic energy iv. Volume Control Wheel (VCW) - used to adjust gain usually over a range of 0 to 20 or 30 dB range( for some HAs the VCW also controls the HA’s maximum output) b. Internal Controls:
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i. Tone, frequency response, or noise suppression control - change the frequency response ii. Output limiting, power, SSPL-90, or maximum output control - control the maximum output iii. Peak clipping - as the input increases the output increases in a linear manner until a maximum output level is reached iv. Compression -most desirable way to control output
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