Final Eartell production in action
I connected the eartell product and collected data from 5 different microphones, I passed sound from various angles and at various heights and collected the data, I found that the average ITD between the amplifiers in 0.12 and the ITD from end to end microphones is 0.6msec, I converted the analog signal into sound pressure level db using a standard formula now based on the sound source and the sound signal it received my custom program will automatically adjust the ITD and mix it. I still need to add the mixer circuit which will be part of the end product.
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Finalizing and securing microphones
Final Product: After lot of thinking and trying I ended up using the clips tied with zip on one side inserted into a bone conduction headphones, it does capture the sound now from all directions and the data is retrieved for a mixer circuit, The data is then extracted as a file and manipulated using audacity software. After multiple iterations of the sound recording and mixing, I am able to find the perfect spot for the TDOA.
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From Patent Drawing To Reality
Assembling 5 Mic’s to a processor:
Assembling all the mic’s into one processor so that the processor can modify the signals based on the need and then mix into one output to relay into the other ear through bone conduction headphones.
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Mixing audio signals from 5 different mic receivers
Mixing Audio signals from 5 mic’s:
I am placing the mic’s in 5 different angles so that they cover the sound signals from all 5 directions, left and right ear, left and right head curvature, one in the center back of the head.
Mix Sound signals after editing to adjust ITD:
All the 5 mic’s capture the sound and the sound signal is mixed into one audio source, once it is mixed into one audio source it becomes mono and it is difficult to adjust the sound based on the ITD and direction of the sound.
Mix Sound signals before editing to adjust ITD:
All these capture the sound signal and the sound signal will be modified based on the proprietary algorithm. Once the final signal is available it will be outputted into a single audio. Processor knows the source and direction of the sound, it can calculate the time difference, sound pressure and intensity for the same frequency from each of the audio signal. Hence I decided to adjust the sound signals and then mix into one for transmission through bone conduction.
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Testing Interaural Time Delay
Interaural Time Delay:
The interaural time difference (or ITD) when concerning humans or animals, is the difference in arrival time of a sound between two ears. It is important in the localization of sounds, as it provides a cue to the direction or angle of the sound source from the head. If a signal arrives at the head from one side, the signal has further to travel to reach the far ear than the near ear. This pathlength difference results in a time difference between the sound’s arrivals at the ears, which is detected and aids the process of identifying the direction of sound source.
Calculating ITD using a mannequin head, But the results vary based on the obstruction object. So the values that are calculated using mannequin head might not be exact as a human tissue but we can estimate based on the angle of sound, direction and sound pressure.
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Adding bluetooth to the project
Adding a new I2c bluetooth receiver:
Purchased HM10 bluetooth master/slave module and connected to the board I2C pins for transfering the audio to another bluetooth paired device. Since there is no audio codec in the device it cannot really transfer the sound. but it can send the audio data received from A0 and A3 pins through the bluetooth transmitter.
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Connecting multiple microphones to a single processor
Connected multiple microphones to the IO Expansion board with arduino nano processor inside. Changed the program to read the values from multiple microphones and I noticed that there is a difference of 4 db in sound when we speak onto either direction. If we speak into right left side microphone shows value of 4db less than right and vice versa.
Microphones are connected to the bone conducting headphones to simulate human head.
New Arduino Sketch that reads input from two microphones.
//size of the window
const int inputWindow = 100;
// placeholder for a single measurement
unsigned int inputSample1;
unsigned int inputSample2;
void setup() {
// initializing the analog input
//pinMode(inputPin, INPUT);
// initializing the serial communication
Serial.begin(9600);
}
void loop() {
// two variables for minimum and maximum values in window
unsigned int inputMax1 = 0;
unsigned int inputMin1 = 1024;
unsigned int inputMax2 = 0;
unsigned int inputMin2 = 1024;
// loop for the window
for (unsigned int i = 0; i < inputWindow; i++) {
// read in a single value
inputSample1 = analogRead(A0);
inputSample2 = analogRead(A3);
// get the minimum and maximum value
inputMin1 = min(inputMin1, inputSample1);
inputMax1 = max(inputMax1, inputSample1);
inputMin2 = min(inputMin2, inputSample2);
inputMax2 = max(inputMax2, inputSample2);
}
// send the values on serial
Serial.print(“Min Mic 1 : “);
Serial.print(inputMin1);
Serial.print(” Max Mic 1 : “);
Serial.print(inputMax1);
Serial.print(” Diff Mic 1 :”);
Serial.print(inputMax1 – inputMin1);
Serial.println();
Serial.print(“Min Mic 2 : “);
Serial.print(inputMin2);
Serial.print(” Max Mic 2 : “);
Serial.print(inputMax2);
Serial.print(” Diff Mic 2 :”);
Serial.print(inputMax2 – inputMin2);
Serial.println();
}
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Connection with IO Expansion Board
In order to simulate multiple microphones, we need to have multiple ground and VCC pins, it is not possible with arduino uno board without using a IO expansion board.
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Converting Microphone from Omni Directional to Directional Microphone
Omni Directional Microphones: These microphones can respond to sound from all directions.
Directional Microphones: These microphones can respond to sound at a fixed angle. These are used in noise cancellation.
Eartell: It is important to convert omni directional to directional microphones in order to know the direction of the sound so that eartell can process the sound signal and distribute to the good ear.
Experiment: I purchased 4 funnels and then sliced the end so that the microphone perfectly fits inside the funnel, I tried the program (refer to my previous blog fro the program) to see if it is really working but it is still able to respond to the sound from all angles but it is little weak, I need to cover the funnel using a sound proof tape.
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