The remarkable ability of the human ear to locate sounds in the surrounding environment is usually attributed to the use of both ears, which detect and interpret auditory cues. However, recent studies have suggested that people with monaural hearing, or hearing loss in one ear, can also perceive sound location using differences in loudness or arrival time of sounds at the one ear.
A team of researchers from the Japan Advanced Institute of Science and Technology (JAIST) and Toyama Prefectural University has proposed a new method to estimate the direction-of-arrival (DOA) of sound signals in three dimensions. The study, published in the journal Applied Acoustics, explains that the technique uses monaural cues to estimate DOA and can help simplify microphone array designs.
The human ear can locate sounds in the surrounding environment using both ears to detect and interpret auditory cues. However, people with monaural hearing, or hearing loss in one ear, can still perceive sound location using differences in loudness or arrival time of sounds at each ear.
The researchers used artificial amplitude modulation noise and human speech signals to simulate sound signals from different directions while accounting for the effect of the ears, torso, and head in filtering sound. They then obtained the monaural modulation spectrum (MMS) of the signals, describing their frequency modulations to identify key features tied to DOA.
To avoid monaural front-back confusion, the team considered the effect of head movement on the MMS to realize a more accurate DOA estimation. Using the known DOA and the features of the MMS as training data, they constructed a polynomial regression model that estimated the DOA from the MMS features of the sound signal in terms of the horizontal and vertical direction of the listener.
The model was able to accurately estimate the DOA of 829,440 speech signals, outperforming even human monaural hearing. However, the researchers suggest 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’s implications could lead to advancements 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”
–Prof. Masashi Unoki, Lead Researcher
In addition, the capability to estimate the sound direction using monaural cues could help remove limitations on the design and positioning of audio recording devices and microphone arrays. This can help avoid poor sound quality resulting from inadequate microphone array design or positioning.
Overall, the researchers’ proposed method represents an impressive advancement in monaural sound localization that could have a significant impact on various industries in the future.
- Rui Wang, Nguyen Khanh Bui, Daisuke Morikawa, Masashi Unoki. Method of estimating three-dimensional direction-of-arrival based on monaural modulation spectrum. Applied Acoustics, 2023; 203: 109215 DOI: 10.1016/j.apacoust.2023.109215
Source: JAIST, Applied Acoustics
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