In Section 7, we propose, and in Section 8, we implement our TDE-ILD-HRTF-based method for 2D whole-plane and three-dimensional (3D) entire-space sound source localization. Section 6 includes simulation of this method for 2D cases, where according to simulation results and due to the use of ILD, we introduce source counting. Section 5 covers the introduction of TDE-ILD-based method to two-dimensional (2D) half-plane sound source localization using only two microphones. In Section 4, we explain sound source angle of arrival and location calculations using ILD and PHAT. After a literature review, we explain HRTF-, ILD-, and TDE-based methods and discuss TDE-based phase transform (PHAT). The structure of this paper is as follows. Here, we intend to introduce a real-time accurate wideband sound source localization system in low degree reverberation far-field outdoor cases using fewer microphones. Therefore, reduction of the number of microphones is very important, which in turn leads to reduced localization accuracies using conventional methods. Moreover, outdoor high-accuracy sound source localization in different climates needs highly sensitive and high-performance microphones which are very expensive. Also, many such sound source signals are wideband signals. Furthermore, our experiments confirm that placing localization system in suitable higher heights often reduces the reverberation degree, especially for flying objects. For localizing such sound sources, a far-field assumption is usual. Our goal is real-time sound source localization in outdoor environments, which necessitates a few points to be considered. Source localization has been one of the fundamental problems in sonar, radar, teleconferencing or videoconferencing, mobile phone location, navigation and global positioning systems (GPS), localization of earthquake epicenters and underground explosions, microphone arrays, robots, microseismic events in mines, sensor networks, tactile interaction in novel tangible human-computer interfaces, speaker tracking, surveillance, and sound source tracking. Experimental results indicate that our implemented method features less than 0.2 degree error for angle of arrival and less than 10% error for three-dimensional location finding as well as less than 150-ms processing time for localization of a typical wideband sound source such as a flying object (helicopter). The simple microphone arrangement used leads to linearization of the non-linear closed-form equations as well as no need for initial guess. A special reflector is designed to avoid mirror points and source counting used to make sure that only one dominant source is active in the localization area. Our proposed TDE-ILD-HRTF method tries to solve the mentioned problems using source counting, noise reduction using spectral subtraction, and HRTF. We apply this method to outdoor cases and propose a novel approach for N-dimensional entire-space outdoor far-field and low reverberation localization of a dominant wideband sound source using TDE, ILD, and head-related transfer function (HRTF) simultaneously and only N microphones. Also, using a linear array, two mirror points are produced simultaneously (half-plane localization).

However, ILD-based methods need only one dominant source for accurate localization. Combined TDE and intensity level difference or interaural level difference (ILD) methods can reduce microphone counts to two for indoor two-dimensional cases. These methods need numerical analysis to solve closed-form non-linear equations leading to large computational overheads and a good initial guess to avoid local minima. Time delay estimation (TDE)-based methods are common for N-dimensional wideband sound source localization in outdoor cases using at least N + 1 microphones.

Reduction of the microphone count is our goal. Outdoor sound source localization in different climates needs highly sensitive and high-performance microphones, which are very expensive. This paper investigates real-time N-dimensional wideband sound source localization in outdoor (far-field) and low-degree reverberation cases, using a simple N-microphone arrangement.

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