The ReSound AZURE is the latest state of the art hearing instrument from the company that introduced the first open fitting hearing aid to the industry. The ReSound Air (which since has been discontinued) brought the concept of natural feeling open fittings to the public about five years ago. Nearly all of the major manufacturers now offer open fitting hearing aids.
This new hearing instrument from ReSound boasts of Natural Sound, Natural Amplification and Natural Awareness. Natural Awareness is a new concept in directionality for hearing aids. Research has shown that the most commonly used directional systems are unsatisfactory to many users. Even in hearing aids that automatically switch from directional to omnidirectional based on decision logic within the hearing aid, users find many times that they want to hear something that the hearing aid has decided to suppress. Two hearing instruments set in directional mode listening to the front are preferred in only 1/3 of listening situations.
Instead of suppressing the sound behind the listener, the AZURE Natural Directivity has one hearing instrument set in the omnidirectional mode and the other instrument focused on sounds from the front. This concept is similar to monocular contact lenses, where one lens is focused for near objects and the other is set for far vision. The brain sorts all of this out and the user finds that he can read and see objects at a distance. The same idea is behind the AZURE hearing instruments. One hearing aid listens for sounds all around the user while the other focuses on sounds from the front. The brain sorts this out and allows the user to feel that he can hear the person in front of him withought any sense of isolation from events happening behind or beside him.
ReSound states that this Natural Directionality offers the same speech intelligibility as static systems with both hearing aids in directional mode all of the time, and allows the user overall listening ease in all situations. This reduces the worry that something important is happening behind you. As opposed to hearing aids that must be switched into and out of directional mode, ReSound states that their Natural Directivity keeps the user in the optimal listening mode, maximizing speech intelligibility at all times.
This Natural Directivity idea requires special hearing aid programming software and special testing by the audiologist to properly set the hearing aids’ action to be transparent for the user. The software used a decision tree to select the focus ear (directional) and the monitor ear (omnidirectional).
The software applies different gain to the omnidirectional and directional instruments, and applies algorithms to keep the instruments balanced. The algorithms apply different gains for near and far sound fields. This whole concept of natural directivity came out of a 2004 Walter Reed Army Medical Center award winning study.
As you know from this web site, most digital hearing aids use the Fast Fourier Transform (FFT) to allow processing of sound in the frequency domain. The typical digital hearing aid listens for a short period of time, then uses the FFT algorthm to look at the signal as amplitude versus frequency. The hearing aid perfoms its processing on this frequency spectrum (perhaps boosting the high frequencies and removing nose signals) the uses the FFT altorthm to convert the spectrum back to the amplitude versus time spectrum of normal sound. This allows very complex operations on the signal, but at the cost of some delay between the hearing aid output versus its input. This delay is partly because of the required sampling interval and partly by the two FFT transformations and circuit delays. This can get to be a problem when the user can hear the input signal as well as the output signal (he will hear a slight echo).
When ReSound intorduced the AIR open fitting hearing aid several years ago, this problem was quite apparent,. The open fitting did not use an ear mold, just a plastic pipe caring the sound into the ear. Since the ear was open to other sounds, people with reasonalbly good hearing could hear the quiet original sound and the delayed amplified sound. This really wouldn’t work, so ReSound swiched from the FFT type of process to another digital processer, the WARP processor
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