Amp Ch 10 week 5 lecture (quiz for week 7)

What is a transducer?

A device that converts one form of energy into another; in hearing aids, microphones and receivers are transducers.

What is the function of a hearing-aid microphone?

It converts acoustic sound energy into an electrical signal.

What is the function of a hearing-aid receiver?

It converts the electrical signal back into acoustic energy and acts as a miniature loudspeaker.

What is the function of the power supply?

It provides the electrical energy needed for the hearing aid to operate.

What is frequency-response shape?

The relative signal level or gain provided across different frequencies.

What is a flat frequency response?

Equal energy or gain across frequencies.

What is bandwidth?

The range of frequencies included in a signal or system.

What is a filter?

A device or process that changes the frequency-response shape by allowing some frequencies to pass while reducing others.

What is an amplifier?

A device that increases the electrical signal; the increase in dB is called gain.

What is distortion?

The introduction of a signal component that was not present in the original signal.

What are voltage, current, and resistance?

Voltage is electrical potential difference, current is the flow of electrical charge, and resistance opposes current flow.

What is Ohm’s law?

I = V/R, where current equals voltage divided by resistance.

What is the difference between DC and AC?

DC flows in one direction, while AC changes direction over time.

What is capacitance?

The ability to store electrical charge as a voltage difference between conductive plates separated by a nonconductive material.

How does a capacitive microphone convert sound into an electrical signal?

Sound moves the microphone diaphragm, changing the distance between conductive plates and therefore changing capacitance and voltage.

What is an electret microphone?

A microphone containing a permanently charged material, eliminating the need for a separate power supply to maintain the charge.

Why were electret microphones useful in hearing aids?

They were small, durable, and did not require a separate charge-producing power supply.

What are MEMS microphones?

Very small silicon-based microphones with a diaphragm, backplate, and structures that control movement and damping.

Why are multiple MEMS microphones used in some hearing aids?

Multiple microphones allow directional processing and improved estimation of speech and noise.

What factors affect microphone input quality?

An unobstructed microphone opening, accurate acoustic-to-electrical transduction, and keeping the input within the front-end input range.

What happens if sound exceeds the front-end input ceiling?

Distortion occurs before the signal reaches later processing, and later gain, compression, or output limiting cannot restore the distorted signal.

What is electromagnetic induction?

A changing magnetic field can induce a current or voltage in a nearby conductor or coil.

How does a telecoil use electromagnetic induction?

It detects changing magnetic fields and converts them into an electrical signal that can be processed by the hearing aid.

What factors affect telecoil sensitivity?

The number of coil turns, coil orientation, and proximity to the magnetic source.

What is near-field magnetic induction?

Wireless energy or signal transfer through a magnetic field over relatively short distances.

What is the advantage of near-field magnetic induction?

It can be energy efficient, but its effective distance is limited.

How does a hearing-aid receiver produce sound?

Electrical current through the receiver coil produces magnetic forces that move the diaphragm and create sound.

Why do receiver designs differ for different hearing aids?

Receiver design affects output, bandwidth, efficiency, size, and power requirements.

Why are larger receiver diaphragms useful for low frequencies?

Low frequencies require greater diaphragm movement, which is easier with a larger diaphragm.

What is a transistor?

An electronic component that can control electrical current and can be used for amplification or switching.

What is a Class A amplifier?

An amplifier design in which current flows continuously; it is simple and small but relatively inefficient and can drain batteries.

What is clipping?

Limiting of a signal because the system cannot provide additional output, which introduces distortion.

What is digital clipping?

Distortion caused when a digital signal exceeds the available numerical range or finite word length.

What is a Class D amplifier?

A highly efficient switching amplifier that uses high-frequency pulses to control output.

Why is Class D amplification useful in hearing aids?

It provides high efficiency, low no-input current drain, and can produce substantial output from a small device.

How does pulse-width modulation represent output level?

Wider pulses represent a higher target output.

How does pulse-density modulation represent output level?

A greater number of pulses per unit of time represents a higher output.

What is RF?

Radio-frequency electromagnetic energy used for wireless communication.

How does RF wireless communication work?

Information is placed onto a high-frequency carrier, transmitted, received, and then demodulated to reconstruct the signal.

What is frequency modulation?

A method in which the frequency of a carrier changes according to the input signal.

What is frequency-hopping spread spectrum?

A wireless method that rapidly changes the carrier frequency among multiple frequencies to reduce interference.

What is Bluetooth?

A wireless communication technology used for short-range personal-area communication.

Why was traditional Bluetooth difficult to use for hearing-aid audio?

It could require too much power and introduce too much delay for hearing-aid applications.

What is Bluetooth Low Energy?

A lower-power version of Bluetooth that supports wireless communication and audio applications.

What is Auracast?

A broadcast technology that allows compatible devices to receive the same wireless audio transmission.

What is digital signal processing?

The analysis and modification of digitally represented signals using mathematical algorithms.

What is an algorithm?

A defined group of mathematical operations used to analyze or modify a signal.

What happens to a signal in a digital hearing aid?

The microphone captures sound, the signal is converted from analog to digital, digital algorithms process it, and the processed signal is converted back to analog for the receiver.

What is analog-to-digital conversion?

The process of converting a continuous analog signal into a digital representation through sampling and quantization.

What is digital-to-analog conversion?

The process of converting a digital representation back into an analog electrical signal for the receiver.

What is sampling?

Measuring the amplitude of an analog signal at discrete points in time.

What is quantization?

Assigning sampled amplitudes to discrete numerical levels.

What is binary encoding?

Representing digital information using numerical values expressed in binary form.

Why does digital representation only approximate the original signal?

The signal is represented using discrete samples and quantized numerical levels rather than as a continuously varying waveform.

What is the sampling rate?

The number of samples taken from an analog signal per second.

What is the Nyquist frequency?

One-half of the sampling rate and the highest frequency that can theoretically be represented without aliasing.

What is the Nyquist rate?

A sampling rate at least twice the highest frequency of interest.

What is aliasing?

An error that occurs when a signal contains frequencies above half the sampling rate, causing them to be represented incorrectly.

How is aliasing prevented?

An anti-aliasing low-pass filter removes frequencies above the appropriate range before sampling.

Why does a hearing aid analyze a signal in short segments?

Short segments allow the digital system to analyze how the signal's frequency components change over time.

What is the time domain?

A representation of a signal showing how amplitude changes over time.

What is the frequency domain?

A representation showing the amount of energy present at different frequencies.

What is the Fourier transform used for?

Converting a signal representation between the time and frequency domains.

What is the FFT?

A fast mathematical method for calculating the Fourier transform.

What is a filter bank?

A group of filters that divides a signal into different frequency regions for separate processing.

What is a pass region?

The frequency range a filter allows to pass with relatively little attenuation.

What is an attenuated region?

The frequency range in which a filter reduces the signal.

What is the cutoff frequency?

The frequency marking the transition between the pass region and the attenuated region.

What is filter slope?

The rate at which a filter changes from passing frequencies to attenuating them.

What does a low-pass filter do?

Passes lower frequencies and attenuates higher frequencies.

What does a high-pass filter do?

Passes higher frequencies and attenuates lower frequencies.

What does a band-pass filter do?

Passes a selected range of frequencies while attenuating frequencies outside that range.

What is the difference between a frequency band and a processing channel?

A band is a frequency region, while a channel is a processing region in which the hearing aid can independently apply processing.

What is an IIR filter?

An infinite impulse response filter that can provide efficient filtering but may introduce phase or group-delay differences.

What is an FIR filter?

A finite impulse response filter that can provide linear-phase behavior and minimal phase distortion.

Why can group-delay differences matter?

Different frequencies arriving at different times can produce constructive or destructive interference and alter the resulting signal.

What is microphone noise floor?

The level of unwanted noise generated by the microphone's electrical and acoustic components.

Why is a low microphone noise floor important?

It is especially important when amplifying low-intensity sounds because microphone noise can become audible.

What is directional microphone processing?

Processing that uses differences between microphone signals to favor sound from desired directions and reduce sound from other directions.

What is an omnidirectional microphone?

A microphone that responds relatively equally to sounds from different directions.

What is a directional microphone?

A microphone system designed to be more sensitive to sound from some directions than others.

What is fixed delay-and-sum beamforming?

A directional microphone strategy that combines microphone signals using fixed timing relationships to emphasize sounds from a desired direction.

What is adaptive directional processing?

Directional processing that changes its response according to the estimated location of noise or competing sound.

Why can bilateral beamforming improve directional processing?

Signals from both hearing aids can be combined to improve speech/noise estimation and create more directional nulls.

What is a directional null?

A direction in which the microphone system substantially reduces sensitivity.

What is the purpose of a higher-order microphone array?

It can provide more directional nulls and potentially greater directional benefit.

What is gain?

The difference between the input level and the output level, usually expressed in dB.

What is output level?

The total sound-pressure level produced by the hearing aid.

What is linear amplification?

Amplification in which the amount of gain remains essentially the same regardless of input level.

Why is linear amplification problematic for many hearing losses?

A person may need more gain for soft sounds but may find the same gain uncomfortable when sounds become louder.

What is compression?

A process that provides more gain for softer inputs and progressively less gain as input level increases.

Why is compression useful for reduced dynamic range?

It can make soft sounds audible while keeping louder sounds within a more comfortable range.

What is WDRC?

Wide dynamic range compression that typically uses a relatively low kneepoint so compression begins for relatively soft-to-average inputs.

What is AGCi?

Automatic gain control based on the input signal, typically associated with compression beginning at a relatively low input level.

What is AGCo?

Automatic gain control based on the output of the hearing aid, used to control maximum output.

What is a kneepoint?

The input or output level at which compression begins.

What is a compression ratio?

The amount of change in input level compared with the resulting change in output level above the kneepoint.

What does a 2:1 compression ratio mean?

A 10 dB increase in input above the kneepoint produces approximately a 5 dB increase in output.

What does a 1:1 compression ratio represent?

Linear amplification with no compression.

What is attack time?

The time required for the hearing aid to adjust gain after the input becomes sufficiently intense to trigger compression.