DPOAE-Based Ear Testing Using MATLAB and Amplifier

Distortion Product Otoacoustic Emissions (DPOAE) testing is a non-invasive way to assess cochlear health. This technique uses sound frequencies to stimulate the inner ear and measures the resulting otoacoustic emissions, which indicate whether the cochlea is functioning properly. In this project, I developed a custom DPOAE testing device using an amplifier for sound generation and a MATLAB app for signal processing.

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Understanding DPOAE Testing

DPOAEs occur when two pure tones (frequencies $f_1$ and $f_2$) are presented to the ear. These tones interact in the cochlea, producing distortion products—new frequencies that are not part of the original tones. The most prominent distortion product is $2f_1 - f_2$, which is generated by the cochlear nonlinearities. Detecting these emissions helps evaluate the integrity of outer hair cells in the cochlea.

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Why Two Frequencies?

The cochlea responds differently to various frequencies due to its tonotopic organization, where specific regions resonate at specific frequencies:

1. Primary Tones:

   • $f_1$ and $f_2$ are two closely spaced frequencies where $f_1$ (lower frequency) is slightly less than $f_2$.
   • These tones stimulate overlapping regions of the cochlea.

2. Interaction Zone:

   • When the two frequencies are played simultaneously, they interact nonlinearly in the cochlea, creating distortion products.
   • The distortion product $2f_1 - f_2$ is used because it is robust and easily measurable in healthy ears.

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System Design

Hardware Components

1. Amplifier:

   • Amplifies the generated audio signals to ensure the tones are strong enough to stimulate the cochlea.
   • Ensures minimal distortion in the generated signals.

2. Ear Probe:

   • Plays the tones into the ear canal and captures the emitted DPOAE signals using a sensitive microphone.

MATLAB App

The MATLAB app handles the generation, playback, and analysis of the DPOAE signals.

1. Tone Generation:

   • Generates two pure tones $f_1$ and $f_2$ with precise frequency and intensity.

2. Signal Analysis:

   • Records the sound from the ear canal.
   • Performs FFT (Fast Fourier Transform) to analyze the frequency spectrum and detect the presence of $2f_1 - f_2$.

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MATLAB Implementation

Tone Generation and Playback

fs = 44100; % Sampling frequency
t = 0:1/fs:1; % Time vector

f1 = 1000; % First tone frequency in Hz
f2 = 1200; % Second tone frequency in Hz

% Generate tones
tone1 = 0.5 * sin(2 * pi * f1 * t);
tone2 = 0.5 * sin(2 * pi * f2 * t);

% Play tones simultaneously
sound(tone1 + tone2, fs);

Recording and FFT Analysis

% Record the signal from the microphone
recObj = audiorecorder(fs, 16, 1);
disp('Recording... Speak into the microphone.');
recordblocking(recObj, 2); % Record for 2 seconds
disp('Recording complete.');

% Get recorded data
recordedSignal = getaudiodata(recObj);

% Perform FFT
N = length(recordedSignal);
f = (0:N-1)*(fs/N); % Frequency vector
fftSignal = abs(fft(recordedSignal));

% Plot frequency spectrum
plot(f, fftSignal);
xlabel('Frequency (Hz)');
ylabel('Amplitude');
title('Frequency Spectrum');

% Highlight DPOAE at 2f1-f2
dpoae_freq = 2*f1 - f2;
disp(['Expected DPOAE Frequency: ', num2str(dpoae_freq), ' Hz']);

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How It Works

1. Tone Playback:
   The MATLAB app generates and plays two tones, $f_1$ and $f_2$, through an amplifier and into the ear canal.

2. Cochlear Response:
   The cochlea vibrates in response to these tones, producing the distortion product $2f_1 - f_2$.

3. Signal Capture:
   The emitted DPOAE signal is captured by the ear probe and fed back into the MATLAB app for analysis.

4. FFT Analysis:
   The app performs FFT on the recorded signal to analyze its frequency spectrum and detect the presence of the DPOAE at $2f_1 - f_2$.

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Applications

• Hearing Screening: Identify cochlear health in newborns and individuals exposed to loud environments.
• Clinical Diagnostics: Diagnose hearing loss caused by outer hair cell dysfunction.
• Research: Study the mechanics of the cochlea and auditory system.

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Videos

1. Working Video

DPOAE PASS (IN THIS VIDEO AM SHOWING IF I BLOCK THE MICRIOHONE SPEAKERS WILL PLAY THE SOUND AND FULL REFLECTION WILL BE THERE SO WE WILL GET THE ALL GREEN WHICH MEANS EARS  HAVE NO ISSUE ):

DPOAE REFER (IN THIS VIDEO AM SHOWING AM NOT  BLOCK THE MICRIOHONE SPEAKERS WILL PLAY THE SOUND AND BECAUSE OF ZERO REFLECTION WE WILL GET THE ALL RED WHICH MEANS EARS  HAVE ISSUE ):

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2. 3D CIRCUIT DESIGN 

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Conclusion

This DPOAE testing system combines MATLAB's powerful signal processing capabilities with a custom-built amplifier and ear probe to assess cochlear health effectively. By detecting $2f_1 - f_2$ distortion products, we gain valuable insights into the auditory system's functionality, paving the way for advancements in hearing diagnostics and research.