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

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.

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

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

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

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

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): 311-322. von Békésy, Georg. "The moon illusion and similar auditory phenomena."The American journal of psychology 62.4 (1949): 540-552. 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

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

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

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.

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 397.6719 (1999): 517-520.

Signal Path Demonstration

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

Signal Path Demonstration

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

GANTT Chart

Questions?