Electrical audio signal processing systems and devices – Sound effects – Reverberators
Patent
1992-05-26
1994-01-04
Ng, Jin F.
Electrical audio signal processing systems and devices
Sound effects
Reverberators
381 684, H04R 2500
Patent
active
052767396
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention concerns a programmable hybrid hearing aid with digital signal processing and a method for detection and signal processing in a programmable hybrid hearing aid.
Present day hearing aids are usually based on analog amplification of the sound intercepted by the ear. With the aid of present day state of the art, hearing aids of this kind have become miniaturized to such an extent that they can be inserted into the outer meatus, thus constituting so-called "all-in-the-ear" aids. Many people prefer hearing aids of this type for reasons of appearance and comfort, but the use of analog amplification of the sound signal combined with the fact that these hearing aids close off the meatus, make it difficult to obtain an optimum adaptation of the signal to any hearing residue which the person using the hearing aid may still have. Most forms of age-dependent hearing impairment leave a substantial amount of hearing residue in certain frequency ranges. In the case of normal neurologically-dependent hearing impairment the sense of hearing usually remains relatively unimpaired at the lowest frequencies. If the ear is completely closed by the hearing aid, the sound has to be amplified at all frequencies in the audible range. At the same time, the use of ordinary analog amplification makes it difficult to obtain an optimum response function, i.e. a response function which in an appropriate manner simulates the acoustic response of the meatus when it is open without insertion amplification. Any hearing residue which the user may have will result in the amplification in an all-pass band giving rise to discomfort, e.g. if impulse noise and transient acoustic signals are amplified in those frequency bands where the ear still has a reasonably normal degree of hearing. Moreover, an open meatus normally has a resonance of approximately 3 kHz, and this resonance makes a vital contribution to the quality of the auditory impression, since it falls within the range of the formant frequency for normal speech and thus contributes to giving it its tonal qualities, which are tremendously important for the comprehension of speech sound and thus for the person's ability to understand speech.
In order to facilitate the optimum adaptation of the auditory signal to any hearing residue and simultaneously optimize the hearing aid's response function, hearing aids have been developed wherein the signal processing is performed digitally. The response function is adapted through filtering of the digital signal by means of appropriate filter coefficients, thus permitting the frequency response to some extent to simulate the response function of a person with normal hearing. If the aids of the digital type are designed as so-called all-in-the-ear aids, the problem again arises that the meatus is closed, thus preventing any hearing residue which the person may have from being utilized. The response curve can be modified to a certain extent in order to take this into consideration. As a rule, however, it will be an advantage to have several response curves, in order to adapt the hearing aid's amplification as a function of the frequency to a variety of acoustic environments. It is obvious, e.g., that it would be considerably more difficult to understand normal speech which is embedded in loud background noise, in which case it will be natural to generate a response function which gives priority to amplification in the range of the speech signal's formant frequencies, i.e. primarily in the range from approximately 1 up to approximately 4 kHz.
Another well-known problem with hearing aids, whether they are digital or analog, is acoustic feedback between sound generator and microphone. Even though the hearing aid is positioned so that it closes the meatus and thus also prevents utilization of any hearing residue, this does not prevent feedback at high amplification, since the sound from the sound generator can be conducted back to the microphone either via the material of the hearing aid or via tissue and bone mat
REFERENCES:
patent: 4750207 (1988-07-01), Gebert
patent: 4947432 (1990-08-01), Topholm
Krokstad Asbjorn
Ramstad Tor A.
Svean Jarle
Ng Jin F.
NHA A/S
Tran Sinh
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