Monaural Hearing Breakthrough: 3D Sound Location Possible

Author: Japan Advanced Institute of Science and Technology
Published: 2023/03/15 - Updated: 2025/09/26
Publication Details: Peer-Reviewed, Research, Study, Analysis
Category Topic: Deafness and Hearing Loss - Academic Publications

Page Content: Synopsis - Introduction - Main - Insights, Updates

Synopsis: This peer-reviewed research from the Japan Advanced Institute of Science and Technology presents a groundbreaking method for three-dimensional sound localization using monaural modulation spectrum (MMS) analysis, demonstrating that individuals with hearing in only one ear can achieve remarkably accurate sound direction detection. The scholarly work, published in Applied Acoustics, establishes that while people typically rely on binaural hearing cues from both ears, monaural listeners can effectively locate sound sources by analyzing frequency modulations in received signals, accounting for how the head, torso, and ears naturally filter incoming audio. The research team developed a polynomial regression model that successfully estimated sound direction for over 829,000 speech signals, actually outperforming typical human monaural hearing capabilities and addressing the common front-back confusion problem through head movement analysis.

This authoritative research proves invaluable for individuals with single-sided deafness, hearing aid manufacturers, and audio engineers, as it reveals the sophisticated sound localization abilities that exist within monaural hearing and opens pathways for enhanced assistive technologies and simplified microphone array designs - Disabled World (DW).

Introduction

Method of Estimating Three-Dimensional Direction of Arrival Based on Monaural Modulation Spectrum - Applied Acoustics

The ability to locate sounds in the surrounding environment is a remarkable feature of the human ear. Typically, people with good hearing use both ears to detect and interpret auditory cues. Differences in the loudness or arrival time of sounds at each ear provide us with vital information about the location and direction of the sound source. Interestingly, however, studies have suggested that while binaural cues are sufficient for sound localization, they are unnecessary. People with monaural hearing (hearing loss in one ear) can perceive sound location as well.

Main Content

Fortunately for engineers, this can help remove limitations on the design and positioning of audio recording devices and microphone arrays. For source localization and noise reduction, microphone arrays must be placed at specific intervals and positions to capture and analyze sound from different directions effectively. To avoid poor sound quality resulting from inadequate microphone array design or positioning, the capability to estimate the proper direction using monaural cues is highly desirable as it can help simplify microphone array designs.

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Researchers from Japan propose a method for estimating sound direction from monaural hearing that takes into consideration how an individual’s head, torso, and ears affect their perception of the sound source - Image Credit: Masashi Unoki from JAIST.
Researchers from Japan propose a method for estimating sound direction from monaural hearing that takes into consideration how an individual’s head, torso, and ears affect their perception of the sound source - Image Credit: Masashi Unoki from JAIST.
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In a study made available online on 13th January 2023 and published in the journal Applied Acoustics on 28th February 2023, Prof. Masashi Unoki and his colleagues from the Japan Advanced Institute of Science and Technology (JAIST) and Toyama Prefectural University, Japan, have proposed a method that uses monaural cues to estimate the direction-of-arrival (DOA) of sound signals in three dimensions.

"In our work, we propose an estimation method based on monaural modulation spectrum (MMS), which relies on modulation in the frequency spectrum of the received signal to detect the signal DOA. This can help us develop monaural cues for single-channel signal processing," explains Prof. Unoki.

To determine the monaural DOA, the team simulated sound signals from different directions using artificial amplitude modulation noise and human speech signals while accounting for the effect of the ears, torso, and head in filtering sound. Next, they obtained the MMS of the signals describing their frequency modulations to identify key features that could be tied to the DOA of the signals. To avoid monaural front-back confusion, which occurs when sound sources at the same angle in front of or behind the listener can produce the same estimates for the DOA, the researchers considered the effect of head movement on the MMS to realize a more accurate DOA estimation.

Continued below image.
The proposed model is trained to estimate the DOA of sound signals based on the extracted features of the monaural modulation spectrum of the signal - Image Credit: Masashi Unoki from JAIST.
The proposed model is trained to estimate the DOA of sound signals based on the extracted features of the monaural modulation spectrum of the signal - Image Credit: Masashi Unoki from JAIST.
Continued...

Using the known DOA and the features of the MMS as training data, they then constructed a polynomial regression model that estimated the DOA from the MMS features of the sound signal in terms of the horizontal and the vertical direction of the listener. The model could accurately estimate the DOA of 829,440 speech signals, outperforming even human monaural hearing.

While the team qualifies their findings by suggesting that there is more work to be done to account for background noise and individual differences in ear shape when creating the model, the study demonstrates an impressive advancement in monaural sound localization. Speculating about its implications, the researchers envision their technology's applications in sound surveillance techniques and hearing aid enhancements.

"Our study will help reveal our ability to localize sounds based on monaural hearing, which, in turn, could stimulate various innovations in hearing aid techniques in the long-term," concludes Prof. Unoki.

About the Study

This study was supported by the Fund for the Promotion of Joint International Research (Fostering Joint International Research (B)) (20KK0233) and JSPS-NSFC Bilateral Joint Research Projects/Seminars (JSJSBP120197416). This study was also supported by the SCOPE Program of the Ministry of Internal Affairs and Communications (Grant No.: 201605002). Authors: Rui Wang, Nguyen Khanh Bui, Daisuke Morikawa, and Masashi Unoki.

Insights, Analysis, and Developments

Editorial Note: While this technical breakthrough offers hope for millions living with single-sided hearing loss, the research also illuminates a profound truth about human adaptability—that our auditory system possesses remarkable compensatory mechanisms we're only beginning to understand. The implications extend far beyond assistive technology, suggesting that perceived limitations in sensory processing may often mask sophisticated biological workarounds that science has yet to fully appreciate or harness - Disabled World (DW).

Attribution/Source(s): This peer reviewed publication was selected for publishing by the editors of Disabled World (DW) due to its relevance to the disability community. Originally authored by Japan Advanced Institute of Science and Technology and published on 2023/03/15, this content may have been edited for style, clarity, or brevity.

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APA: Japan Advanced Institute of Science and Technology. (2023, March 15 - Last revised: 2025, September 26). Monaural Hearing Breakthrough: 3D Sound Location Possible. Disabled World (DW). Retrieved November 15, 2025 from www.disabled-world.com/disability/types/hearing/monaural-direction.php

MLA: Japan Advanced Institute of Science and Technology. "Monaural Hearing Breakthrough: 3D Sound Location Possible." Disabled World (DW), 15 Mar. 2023, revised 26 Sep. 2025. Web. 15 Nov. 2025. <www.disabled-world.com/disability/types/hearing/monaural-direction.php>.

Chicago: Japan Advanced Institute of Science and Technology. "Monaural Hearing Breakthrough: 3D Sound Location Possible." Disabled World (DW). Last modified September 26, 2025. www.disabled-world.com/disability/types/hearing/monaural-direction.php.

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