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A hearing aid should answer two questions: what and where?

Now, a team of researchers at Aalto University has developed a technology to accurately provide the missing directional information. Their work was published in the prestigious Journal of American Society of Acoustics (JASA).

‘Improving the spatial quality of sound is about improving the quality of life,’ says lead author doctoral student Janani Fernandez, who has also worked with cochlear implants. Special expertise in signal processing was brought to the work by another doctoral student, Leo McCormack.

The outer parts of our ears play an important role in determining where a sound is coming from. But with hearing aids, sounds sources seem to fill the head, which is distracting and tiring, especially in crowded situations. This is because the sound captured by the microphone is amplified and then passed through a thin tube directly into the ear canal, losing directional information. Not knowing where sounds come from also makes it more difficult to distinguish between different speakers.

In the JASA paper, the researchers present a signal processing model that analyses data from multiple microphones collecting sound from different directions to capture spatial information. ‘Only then is it passed on, for example to a compressor in a hearing aid, which amplifies the signal to suit the listener’s needs. The sound is then played back to the listener using the analysed spatial information, creating a natural spatial impression,’ says Ville Pulkki, Professor of Acoustics.

Determining the direction of sounds is also a safety issue for the hearing impaired, Fernandez stresses. ‘For example, it’s important to distinguish which direction a car is coming from when crossing a road.’

Authentic surround sound would also make augmented reality (AR) experiences more realistic and enjoyable. For example, if a symphony orchestra concert were recorded with enough microphones placed in different parts of the concert hall, the new model could reproduce it so accurately that music fans wouldn’t have to travel to Berlin, London or Chicago to hear top orchestras.  ‘A VR concert would offer the same experience as a concert hall,’ says Fernandez.

The study also involved the University of Tampere.

(asa.scitation.org)