MULTICHANNEL AND MULTI-MICROPHONE DIRECTIONAL HEARING AIDS: Fitting Procedures and Evaluation of Current and Emergent Technology

The most common complaint of those who wear hearing aids, by far, is interference from background noise and reverberation (e.g. echoing environments). The RERC for Hearing Enhancement has been working on techniques for reducing the effects of background noise and reverberation on speech clarity. Thus far, improvements shown with single microphone input are small, if any. However, relatively good improvements in clarity have been seen when more than one microphone is used (Levitt et al, 1990; Levitt et al, 1993, Schwander and Levitt, 1987; Weiss, 1987).
     

  • This project will evaluate current multichannel and multi-microphone hearing aid technology, as well as emerging technology, for integration into more advanced versions of 
    next generation hearing aids.

  • Until recently, most hearing aids increased or amplified all 
    sounds equally, resulting in loud sounds often being too loud 
    and softer ones, too soft. These hearing aids used linear amplifiers. Most of today's hearing aids use compression amplifiers, which adjust sound in varying amounts, depending
     on sound input level. As the input level of sound increases (or sound gets louder) the amount of gain (or amplification) decreases. The amplifier can be set to amplify soft sounds by a greater amount than loud sounds. In multichannel compression hearing aids, the sound or signal to be amplified is split into 2 
    or more channels, thus allowing different amounts of 
    amplification and compression of the signal in different
     frequency (pitch level) regions.

  • While hearing aids with multichannel compression amplification are increasingly available, there are no clear cut guidelines for fitting them. This project will also evaluate fitting procedures for 
    a new general approach to the prescriptive fitting of multichannel hearing aids.

      Experiments 1 and 2:

  • Will evaluate 2 contrasting fitting methods: individualized fitting procedures and new prescriptive procedures for compression amplification.
  • Results will resolve a long-standing conflict within the field regarding the appropriate way to fit multichannel hearing aids, 
    thus laying the foundation for a generally accepted approach to 
    the fitting of multichannel hearing aids.     

      Experiments 2 and 3:

  • Will evaluate promising and emerging technologies, beginning with 2-microphone directional hearing aids, just introduced for clinical use, and moving on to prototype hearing aids with an 
    array of wearable directional microphones.

      Experiment 5:

  • Will further develop a currently emerging 2-microphone adaptive noise cancelling system. With the current rate of progress in 
    digital hearing aids, it is likely that this method of noise reduction could be implemented in a practical hearing aid in the not too distant future.

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