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

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.

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

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

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

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

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

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 1000 4000 10000 Frequency (Hz)

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 397.6719 (1999): 517-520.

Modeling Reverberation Time Initial Delay Early Reflections Later Dense Reflections http://www.acousticalsurfaces.com/acoustic_IOI/101_13.htm http://articles.ircam.fr/textes/Jot97b/

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 http://www.acousticalsurfaces.com/acoustic_IOI/101_13.htm

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

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

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

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

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

GANTT Chart

Questions?