Data-Acquisition Robot for Acoustic Sensing

Work done with Dr. Sumohana Chhannappayya and Dr. K Sri Rama Murty (IIT Hyderabad)

(July 2021 - May 2022)

Overview

Developed a complete robot audition platform for robust and precise sound source localization and tracking in outdoor environments. The system integrates an 8-channel microphone array mounted on a custom-built all-terrain robot with a height-adjustable mast (up to 1.7 m).

Sound Source Localization

The localization pipeline uses the Generalized Cross-Correlation with Phase Transform (GCC-PHAT) algorithm for time-difference-of-arrival (TDOA) estimation between microphone pairs. For microphones \(i\) and \(j\), the GCC-PHAT function is:

\[ R_{ij}(\tau) = \int_{-\infty}^{\infty} \frac{X_i(f) \, X_j^*(f)}{|X_i(f) \, X_j^*(f)|} \, e^{j 2\pi f \tau} \, df \]

where \(X_i(f)\) and \(X_j(f)\) are the Fourier transforms of the signals at microphones \(i\) and \(j\), and \(\tau\) is the time delay. The phase transform normalization makes GCC-PHAT robust to reverberation and noise in outdoor environments.

The TDOA estimates from multiple microphone pairs are combined using Steered Response Power (SRP) to estimate the direction-of-arrival (DOA) of the sound source, scanning over a grid of candidate angles:

\[ P(\theta, \phi) = \sum_{i < j} R_{ij}\!\left(\tau_{ij}(\theta, \phi)\right) \]

where \(\tau_{ij}(\theta, \phi)\) is the expected delay for direction \((\theta, \phi)\) based on the array geometry.

Microphone Array Specifications

Parameter	Value
Channels	8
Array geometry	Uniform circular array (UCA)
Array diameter	0.2 m
Sampling rate	44.1 kHz
Mast height range	0.5 - 1.7 m (adjustable)

Robot Platform

Custom-built all-terrain mobile robot with differential drive
Onboard HDD for live data storage from state estimation and sensor streams
4G LTE communication for remote data streaming and robot control
Integrated IMU, GPS, and wheel encoders for state estimation
ROS-based software architecture for sensor integration and real-time processing