Electrical audio signal processing systems and devices – Hearing aids – electrical
Reexamination Certificate
1994-03-16
2001-01-09
Le, Huyen (Department: 2743)
Electrical audio signal processing systems and devices
Hearing aids, electrical
C381S316000, C381S320000
Reexamination Certificate
active
06173062
ABSTRACT:
The present invention relates to hearing aids for the deaf and the hearing impaired and, in particular, to hearing aid apparatus which utilizes a frequency transposition of signals from the audio frequency range to another frequency range, such as the ultrasonic frequency range, and vibratory transmission to the human sensory system of the frequency shifted signals as a means of communicating with the human sensory system. The present invention also pertains to the frequency shifting of audio frequency range signals from one frequency band to another whereby the audio frequency signals are converted to frequency ranges representing “islands of hearing” in which the hearing perception of certain hearing impaired persons is more acute than at other frequency ranges. The invention further pertains to a method and apparatus for forming a digital single sideband amplitude modulated signal.
BACKGROUND AND PRIOR ART
A hearing aid system of one general type to which the present invention relates is disclosed in U.S. Pat. No. 4,982,434—Lenhardt et al. In the referenced patent, there is disclosed a hearing aid system which utilizes such shifting of signals from the audio frequency range to the ultrasonic frequency range (referred to as “supersonic” frequency range in the patent), conversion of the shifted ultrasonic signal to a vibratory signal, and physical application of the vibratory signal to the human body for communication with the human sensory system. In one embodiment of the invention as disclosed in the referenced patent, an audio frequency signal is amplitude modulated onto an ultrasonic carrier signal for conversion to a vibratory signal and application to the body. In that embodiment, amplitude modulation is carried out by utilizing the analog audio signal as the modulating signal to modulate an analog ultrasonic carrier signal. In such a modulation system, an amplitude modulated signal with double (upper and lower) sidebands is derived.
The referenced system has provided excellent results in permitting the severely hearing impaired and even otherwise totally deaf persons to sense and understand audio frequency communications. It is an object of the present invention to provide even further improvements in systems of the aforementioned type and to provide as well improved apparatus and methods for shifting the frequency of audio frequency signals from one frequency band to another to improve the hearing response of hearing impaired persons who have a more acute hearing response in a frequency range which differs from the normal response in the audio frequency range. It is also an object of the present invention to provide improved digital apparatus and methods for single sideband amplitude modulation for hearing aid applications as well as other applications. Such digital frequency shifting may be either up or down in frequency from the normal audio frequency range and may be into the ultrasonic range as well into other frequency ranges depending upon the hearing response characteristics of the subject.
SUMMARY OF THE INVENTION
The present invention provides further improvements in systems of the aforementioned type by providing a digital system for shifting the frequency of audio signals.
In one embodiment thereof, an apparatus and method in which amplitude modulation utilizing only a single sideband is employed. As will be more fully explained below, it has been discovered that the physiology of the human sensory system is more responsive to a single sideband amplitude modulated signal than a double sideband amplitude modulated signal. The apparatus and method of the present invention also provide improved digital signal processing apparatus and methods for deriving such a single sideband amplitude modulated signal in an efficient manner with a high quality, virtually distortion free and noise free signal. In forming such a high quality digital single sideband modulated signal, the apparatus and method of the present invention function to eliminate signal anomalies which otherwise occur in the digital signal and which deteriorate the quality of the signal. Such improved apparatus and methods are applicable to frequency shifting in hearing aids as well as other applications as will be more fully explained below. In one embodiment of the present invention where only the upper sideband was utilized and the lower sideband was suppressed by more than 60 dB, significant improvements in performance in a hearing aid apparatus were realized.
In addition, the apparatus and method of the present invention utilize an all digital processing technique, which offers advantages in providing freedom from problems common to analog systems such as drift, temperature dependent characteristics and changes in parameters and characteristics with age. In the apparatus and method of the present invention, a digital single sideband amplitude modulated signal is formed in which certain signal anomalies which otherwise cause deterioration in the quality of the signal are virtually eliminated, thus producing a high quality single sideband amplitude modulated signal in digital form.
The digital system of the present invention thus provides a high quality signal which is virtually distortion free and noise free. In addition, the all digital processing system of the present invention allows mechanization of the functions of the system in a more flexible design environment in which different parameters of the signal processing procedures may be adjusted for optimum performance. Further, mechanization of and modifications to the signal processing algorithms, including customization of the same for special applications, can be implemented through software and firmware and through relatively easy to make changes in these elements.
The present invention also provides an improved method and apparatus for translating audiometric frequencies from the normal hearing range to other frequency bands, such as to an ultrasonic frequency band, and, in the process of translation from one frequency band to another, of adjusting the bandwidth of the audiometric signal. For example, when the audiometric signal is translated to a higher frequency, such as to an ultrasonic frequency, the bandwidth of the audiometric signal can be expanded to provide a greater frequency range for the information signal at the higher frequency. This will be beneficial for some users in providing a wider frequency range for the “just noticeable difference” response of the hearing mechanism at the higher frequency range.
REFERENCES:
patent: 4051331 (1977-09-01), Strong
patent: 4156116 (1979-05-01), Yanick
patent: 4284856 (1981-08-01), Hochmair et al.
patent: 4419544 (1983-12-01), Adelman
patent: 4548082 (1985-10-01), Engebretson et al.
patent: 4686705 (1987-08-01), Smith
patent: 5047994 (1991-09-01), Lenhardt et al.
patent: 5285499 (1994-02-01), Shannon et al.
Dibachi Farid
Lippa Arnold S.
Richardson Charles S.
Hearing Innovations Incorporated
Le Huyen
Rothwell Figg Ernst & Manbeck
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