1. FM Hearing-Aid Device Checkpoint 2
Brian Fang | Robert Johnson | Shoman Kasbekar | Zach Kovar | Arif Moktader

2. The Problem
Project Goal: modify an FM radio system in order to maintain a constant signal-to-noise ratio as the distance between the transmitter and receiver changes
Every type of hearing loss is unique
Amplification quality must be maintained throughout
Ambient noise can hinder the ability to properly focus
The FM system must be able to provide some sort of acoustic cue so that the user can understand where the sound originates
It is well documented that improving the signal-to-noise ratio (SNR) for cochlear implant recipients through the use of an FM system improves speech recognition significantly in the presence of background noise.

3. Needs Assessment Phonak’s current Dynamic FM system
Transmitter to receiver distance detection capabilities
Applying ambient noise to the equation and ensuring our filter can distinguish that sound
Focus is centered on bandpass filters
Computer algorithms to process detected signal
Implementing our system on an Arduino to demonstrate SNR on Design Day

4. Design Components Signal Filter Microphone Receiver Hearing Aid
Transmits signal to
Signal Filter
Microphone
Receiver
Transmits filtered signal to
Transmits signal to
Transmits signal to
Transmits distance data to
Hearing Aid
Transmitter
Receives signal from
Detects distance from
Receives filtered signal from
Located close to
User
Detector
Speaker

5. Project Progress Code in development Arduino research
MATLAB → C
Arduino research
Researching several possible filtering methods

6. Perception of Distance
Intensity
Frequency Spectrum
Reverberations
Binaural Effect
Type of Stimulus

7. Perception of Distance
Mershon, Donald H., and John N. Bowers. "Absolute and relative cues for the auditory perception of egocentric distance." Perception 8.3 (1979):
von Békésy, Georg. "The moon illusion and similar auditory phenomena."The American journal of psychology 62.4 (1949):
Perception of distance varies between people
Find average perception through clinical
Allow mapping to personal perceptions
Auditory horizon
Difficulty in perception past certain distances
Localization
Perception changes above and below the horizontal
binaural

8. Frequency Spectrum Cues
Known: frequency plays “dual role” at different distances
Valid at distances less than 5 feet (spherical sound field)
u = particle velocity, r = distance from center of spherical sound field, c= velocity of sound, f(t) = flow velocity
Since an increase in f(t) causes sound to appear closer, an increase in relative low frequency content of stimulus causes stimulus to seem closer than reality
At greater distances, field must be modeled as a plane
dB absorption per 100 ft. 0.2 dB for 1000 Hz, -1 dB for 4000 Hz, -4.7 dB for 10,000 Hz
As sound comes nearer, auditory system increasingly weighs low- frequency components. For unfamiliar sounds at fixed distances, a reduction of high-frequency components causes an increase in apparent distance of the sound.
high frequencies are attentuated more rapidly than are low frequencies. At successively greater transmission distances the frequency spectrum f complex signals shows a progressive loss of the high-frequency components.
A loss of high frequencies is expected to result in an increased perceived distance for a sound, if that sound is already perceived to be far from the observer. If the sound is already perceive to be close, results in decreased perceived distance
Therefore, an increase in the low-frequency content of the stimulus (relative to the high-frequency content) should cause the stimulus to appear closer, and a decrease in low-frequency content relative to higher frequencies should cause the stimulus to seem more distant

9. Frequency Spectrum Cues
Distant sounds - high frequency attenuation resulting in exponential loss (dB):
R-R0 = distance, a values = absorption coefficients
Attenuation of HF results in increased perceived distance for a sound
Dual role - relatively greater high-frequency content indicates a closer sound source at far distances
Research still being performed into numerically representing frequency, amplitude phenomena
dB absorption per 100 ft. 0.2 dB for 1000 Hz, -1 dB for 4000 Hz, -4.7 dB for 10,000 Hz
As sound comes nearer, auditory system increasingly weighs low-frequency components. For unfamiliar sounds at fixed distances, a reduction of high- frequency components causes an increase in apparent distance of the sound.
A loss of high frequencies is expected to result in an increased perceived distance for a sound, if that sound is already perceived to be far from the observer. If the sound is already perceive to be close, results in decreased perceived distance
Therefore, an increase in the low-frequency content of the stimulus (relative to the high-frequency content) should cause the stimulus to appear closer, and a decrease in low-frequency content relative to higher frequencies should cause the stimulus to seem more distant

10. Reverberation Significant factor for absolute distance cue
Reverberation increases distance
Reverb energy / Direct energy
Bronkhorst, Adelbert W., and Tammo Houtgast. "Auditory distance perception in rooms." Nature  (1999):

11. Reverberation (cont.) ds is the perceived distance
rh is distance where reverb energy = direct energy
A, G, and k are constants derived from experiment
tw is audio time duration
V is room volume
T is reverberation time
Consider virtual room shape and size
Bronkhorst, Adelbert W., and Tammo Houtgast. "Auditory distance perception in rooms." Nature  (1999):

12. Signal Path Demonstration

13. Signal Path Demonstration
Distance scalar is an input that modifies these filters
fft
ifft
These will be pointwise multiplied

14. Signal Path Demonstration

15. Initial Arduino Plans Needed Usage Arduino Uno Breadboard/wires
8-bit DAC: to model various amplitudes
Usage
Use an interrupt on the Arduino to pass in sound
Discrete values will be written in code
DAC will output different voltage levels at our chosen sampling rate

16. GANTT Chart

17. Questions?