1. FM Hearing-Aid Device Checkpoint 3
Brian Fang | Robert Johnson | Shoman Kasbekar | Zach Kovar | Arif Moktader

2. The Problem
Existing FM hearing aid systems send a mono signal from the microphone to both hearing aids
For the hearing impaired ambient noise can hinder the ability to properly focus on a sound source
Project Goal: Create a system of acoustic cues that modify a mono audio signal using distance information to help users 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. Clinical Need Primary Need - classroom pediatric use
1% of children have significant hearing loss: approx. 750,000 individuals
FM system devices strongly impact learning level, interest, etc.
$400-$1000 additive price point
Secondary Need - general adult use
Currently used by small percentage of adults
Phonak - “underuse due to lack of selection criteria”
Future use - determination of standards, marketing will lead to growth

4. Needs Assessment Phonak’s current Dynamic FM system
Transmitter to receiver distance detection capabilities
Focus is centered on bandpass filters
Also considering reverb and binaural effects
Computer algorithms to process detected signal
Implementing our system on an Arduino Uno for Design Day

5. Project Progress MATLAB code almost finished
Significant progress with the conversion of code into C
MATLAB coder possibilities
Filter research completed - can be dropped into MATLAB in the next week
Reverb research continuing, can start designing in MATLAB/C
Arduino Uno purchased

6. MATLAB Code Status Debugging almost completed
Successfully applies a filter to the first frame of the sound file, uses original frames for the rest
Filter code takes an input of a distance
Space along the process for reverb to be dropped in later

7. Frequency Spectrum Cues
Known: frequency plays “dual role” at different distances
nearby sounds: greater low-frequency content causes sound to appear nearer
distant sounds (>5 feet) greater high-frequency content causes sound to appear nearer
Loss expressed in dB at various distances
R-R0 = distance, a values = absorption coefficients
Previous experiments have standardized values
Adapted for typical classroom conditions
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

8. Frequency Spectrum Cues
Result: dB absorption values relating frequency and distance
Will apply results of experimental findings into frequency filter
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
Frequency (Hz)

9. 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):

10. Modeling Reverberation Time
Initial Delay
Early Reflections
Later Dense Reflections

11. Reverberation Coefficients of Materials
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Carpet - Heavy, on Concrete
0.02
0.06
0.14
0.37
0.60
0.65
Brick - Unglazed, Painted
0.01
0.03
Concrete Block - Light, Porous
0.36
0.44
0.31
0.29
0.39
0.25
Plywood - ⅜” thick
0.28
0.22
0.17
0.09
0.10
0.11
Plaster
0.1
0.05
0.04

12. Reverberation Coefficients of Materials Normalized
Material (Normalized)
125Hz
250Hz
500Hz
1000Hz
2000Hz
4000Hz
Carpet - Heavy, on Concrete
0.03
0.09
0.22
0.57
0.92
1.00
Brick - Unglazed, Painted
0.33
0.67
Concrete Block - Light, Porous
0.82
0.70
0.66
0.89
Plywood - ⅜” thick
0.79
0.61
0.32
0.36
0.39
Plaster
0.71
0.43
0.29
0.21
Average
0.64
0.59
0.52
0.51
0.62

13. Conclusion - Reverb can be approximated by a constant absorption coefficient with a value of .18 (average of all values before normalizing)

14. Translation to C Necessary to run project on Arduino for design day
Side-by-side progress (with slight delay) from MATLAB code
“MATLAB Coder enables design engineers developing algorithms in MATLAB to generate readable and portable C and C++ code”
Not everything is directly compatible

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

16. Arduino Plans (cont.) Prototyping plans Input sound
Ideally, one button to increase “distance”, one decreases
Listener will be using headphones
Spatial effects and panning easily implementable

17. GANTT Chart

18. Questions?