Most hearing aids fail in noisy environments, because they amplify conversation partners and the ambient noise equally. Dr Anton Schlesinger improved the ‘hearing glasses’ that work in stereo.
If someone has a hearing loss higher than 35 decibels, he or she is considered to have difficulty understanding speech in silence and is often prescribed a hearing aid to compensate for this. However, the majority (three-quarters) of these people will experience little or no benefit from the hearing aid, because their problem is not understanding speech in silence but rather understanding speech in noise. As a consequence, such people may shy away from public events and risk becoming lonely and isolated. There is little incentive to improve hearing aids, says Dr Anton Schlesinger, because the closed market is dominated by a small number of manufacturers.
The hearing glasses that Dr Marinus Boone (Applied Sciences) developed in the 1990s were an important improvement, because the two microphone arrays situated in the temples allowed smart filters to amplify or suppress sounds depending on their origin. The hearing glasses listened where you looked. Such ‘beamformers’ are known as a robust and practically efficient solution to the speech-in-noise problem. The hearing glasses were brought to market in 2003 by Varibel Innovations.
In his PhD research, Dr Schlesinger has tried to improve the hearing glasses by combining them with smart filters, called CASA filters, for ‘computational auditory scene analysis’. Dr Schlesinger has tested and revised three different types of these filters.
The result was that adding the best type of these postfilters to the two-channel hearing set-up improved the intelligibility of speech in noisy surroundings by 20 to 40 percent. The highest improvement coincides with an increased relative noise level. In other words, the filters work best when needed most. Whether Varibel or other firms will implement the additional filters, Dr Schlesinger cannot say.
He thinks that eventually the hearing aids will become smart enough to judge the surrounding sound and switch to the best matching filters.
Anton Schlesinger, ‘Binaural Model-Based Speech Intelligibility – Enhancement and Assessment in Hearing Aids’, 12 January, PhD supervisors Professor A. Gisolf and Dr Marinus Boone.
