Directionality
What is the horizontal plane?
It refers to the line that goes across the ear and references to the direction where people hear the sound in front of them. This line is typically parallel to the ground, however, can vary in patients with back problems/hunching.
Define an inductor
Inductors (aka coils) store energy in a magnetic field when electric current flows through it
What is the function of recievers?
Converts the amplified/modified electrical signal into an acoustic output signal
What is the name of the code that uses 0's and 1's?
Binary code
What is Nyquist theroem?
States that no information about the signal would be lost if the sampling rate is 2x greater than the highest frequency component presented in a complex signal
What is the difference between omnidirectional microphones and directional microphones?
Omnidirectional microphones: pick up sounds from all directions.
Directional microphones: Directional microphones can focus on signals presented from different directions because it has multiple sound ports/microphones (front and back).
Draw on the board, and explain what peak clipping is
Peak clipping is where the amplifier clips the peaks of the signal
What is an armature?
A thin, bend-able metal piece that moves up and down between magnets
How do you convert the value 432 into binary code?
110110000
Referring to the Nyquist theorem, what causes aliasing?
Aliasing happens when information is lost because the sampling rate is less than twice the highest frequency
Go up to the board and draw a 'hypercardioid' polar plot
Big circle is oriented towards the front (zero degrees).
A smaller circle is behind it and orients towards the back (180 degrees).
What is the difference between THD and IMD?
Inter-Modulation Distortion occurs in harmonics from complex signals.
Name three components of the receiver
-Anchor point
- Magnets
-Diaphragm
-Drive pin
-Coil
-Armature
What do binary numbers represent in digital hearing aids?
The voltage amplitude over a specific period of time
What are modular hearing aids?
Pre-fabricated / "ready-to-wear"
What is null steering?
Nulls are angles of maximum attenuation in the polar plot.
This means that null steering is the ability to move the directionality to best attenuate (decrease) the noise
What is the main difference between Class "A" amplifiers and Class "H" amplifiers?
Class "H" has a variable bias current -- this is important for reducing battery consumption because it no longer stays on consistently for all currents but adjusts to the input of the current.
Draw on the board...the way reciever would be drawn on a blueprint
Triangle on the right of a box
What is the difference between a channel and a band?
Bands are in the hearing aid
Channels are in the programming software
What is HiPro?
It stands for "Hearing Instrument Programmer"
What is the head shadow effect?
The head shadow is a region where sound is reduced in a particular region because it is obstructed by the head.
Decreases the amount of amplification as the input level increases.
What type of converter decodes the binary code and translates it into electrical voltage to be handled by the receiver?
Digital-to-analog converter
What is block processing?
A number of input samples are taken prior to computations, and the Fourier transform is calculated (where the signal is represented in the frequency domain) and is then converted back using the inverse fast Fourier transformation.
Digital hearing aids can process inputs this way
Name one criteria used to evaluate the quality of the digital processor
Instructions per second
Number of bits
Sampling rate
Current consumption
Physical size