Comparative Study of a Parameter Tuned Bioinspired Binaural Sound Source Localization Algorithm and a Standard Beamformer

Abstract

Motivation

Typical devices for sound source localization are acoustic cameras. These consist of an optical camera and a large number of microphones which are used to make a temporal and spatial scan of a sound field. The optical image is then overlaid with colour at the locations of the identified sound sources, according to their loudness. To achieve optimal spatial resolution, many microphones are needed at different distances. For localization of low-frequency sound sources, large microphones distances are also required due to their large wavelength. As an algorithm, especially for real-time applications, the delay and sum beamforming is used.

We want to present an optimized method that is inspired by biology and uses fewer microphones. The parasitoid fly Ormia ochracea is known to be very good at localizing sound events despite its small body size and small distance between its tympanal membranes. This precise directional hearing is due to a mechanical coupling of its auditory canals that consists of masses, springs, and dampers (Miles 1995). This hearing system is well known but tuned to a specific sound source frequency and direction.

As a sound source localization system needs to localize sound sources of a broader frequency spectrum and range of directions. We presented a method to tune the model of the Ormia ochracea’s hearing system  to multiple directions  of incidence (Jünemann 2023a) and to a broader frequency spectrum (Jünemann 2023b).

Research question

How does the bioinspired binaural method based on Ormia ochracea's hearing system compare to a standard beamformer?

Method

In order to compare the novel binaural bioinspired beamformer to a standard beamformer a simulation environment is set up where the sound source location and frequency can be controlled. Two bioinspired binaural beamformers configurations were compared to standard beamformers with 10 or 20 microphones for the following acoustic scenarios. The binaural (2 microphones) configurations where 1) input frequency range of 200 Hz to 2kHz at a microphone distance of d=0.06 m and 2) a input frequency range of 2kHz to 4kHz at a microphone distance of d=0.03 m. For the evaluation of the simulation experiment the angles of incidence where grouped into intervals [1°..10°; 11°..20°; 21°..30°; 31°..40°; 41°..50° ]. The angle of incidence is relative to the centre point of the microphone array. The simulated sound sources were a mixture of 10 or 20 randomly selected frequencies in the specified ranges. Two metrics where selected to analyse the performance of the method. These are the absolute error (AE) of the sound source localization in degree and the 3dB beam width in degree.

Results

Up to the angle of incidence ranges of from [1°..10°] to [21°..30°] the novel bioinspired beamformer performed significantly better than the both of the standard beamformer (10 and 20 microphones). The angle of incidence group of [31°..40°] performed equally well as the standard beamformer with 20 microphones and significantly better than the standard beamformer with 10 microphones. This is a significant result and demonstrates the outstanding performance of the bioinspired beamformer (2 microphones), if the number of microphones must be minimized. For a detailed discussion of the results please refer to the conference paper (Jünemann 2023b).