Because hearing is such a complex sense, the extent of filtering and amplifying required to partially correct an impairment added to the limitations of the hearing instrument by producing distortion and noise. There are five devices which are now available to our patients. Some of these hearing aids samples sound one million times per second, and analyze these signals 32,000 times per second. The computerized digital aids analyze incoming sound, make a determination regarding speech versus noise content, then convert this information to numbers. The potential improvement from digital hearing aids is exciting and far reaching.
Digital sound has minimal distortion.
Researchers at UCSF and around the world are studying the possibilities of such speech enhancement strategies as altering the relative duration of consonants versus vowels, shifting the frequency composition of speech sounds to comply with the individual's hearing impairment, and modifying the transition time between vowels and consonants. These types of procedures are easily accomplished on CDs because the audio signal can be captured, manipulated, and then played back at a later time. With hearing aids, these manipulations must take place instantaneously so that the user of the device does not notice a disparity between visual and auditory cues. In addition, as new algorithms develop, software can be supplied to audiologists so that these improvements can be promptly implemented in the hearing aids without necessitating actual physical changes to the hearing aid itself. However, our experience so far suggests that these systems are indeed superior for certain hearing impaired listeners.