Thursday September 23, 2021’s Smile of the Day: The Hearing Aid
On this Day:
In 1879 Richard Rhodes invented a hearing aid called the Audiophone. But the true history of the hearing aid is a bit difficult to make out…
A hearing aid is a device designed to improve hearing by making sound audible to a person with hearing loss. Hearing aids are classified as medical devices in most countries, and regulated by the respective regulations. Small audio amplifiers such as PSAPs or other plain sound reinforcing systems cannot be sold as “hearing aids”.
Early devices, such as ear trumpets or ear horns, were passive amplification cones designed to gather sound energy and direct it into the ear canal. Modern devices are computerised electroacoustic systems that transform environmental sound to make it audible, according to audiometrical and cognitive rules. Modern devices also utilize sophisticated digital signal processing to try and improve speech intelligibility and comfort for the user. Such signal processing includes feedback management, wide dynamic range compression, directionality, frequency lowering, and noise reduction.
Modern hearing aids require configuration to match the hearing loss, physical features, and lifestyle of the wearer. The hearing aid is fitted to the most recent audiogram and is programmed by frequency. This process is called “fitting” and is performed by a Doctor of Audiology, also called an audiologist (AuD), or by a Hearing Instrument Specialist (HIS). The amount of benefit a hearing aid delivers depends in large part on the quality of its fitting. Almost all hearing aids in use in the US are digital hearing aids. Devices similar to hearing aids include the osseointegrated auditory prosthesis (formerly called the bone-anchored hearing aid) and cochlear implant.
The first hearing aids were ear trumpets, and were created in the 17th century. Some of the first hearing aids were external hearing aids. External hearing aids directed sounds in front of the ear and blocked all other noises. The apparatus would fit behind or in the ear.
The movement toward modern hearing aids began with the creation of the telephone, and the first electric hearing aid, the “akouphone,” was created about 1895 by Miller Reese Hutchison. By the late 20th century, digital hearing aids were commercially available.
The invention of the carbon microphone, transmitters, digital signal processing chip or DSP, and the development of computer technology helped transform the hearing aid to its present form.
The history of DHA can be divided into three stages. The first stage began in the 1960s with the widespread use of digital computers for simulation of audio processing for the analysis of systems and algorithms. The work was conducted with the help of the very large digital computers of that era. These efforts were not actual digital hearing aids because the computers were not fast enough for audio processing in real time and the size prevented them from being described as wearable, but they allowed successful studies of the various hardware circuits and algorithms for digital processing of audio signals. The software package Block of Compiled Diagrams (BLODI) developed by Kelly, Lockbaum and Vysotskiy in 1961 allowed simulation of any sound system that could be characterized in the form of a block diagram. A special phone was created so that a person with a hearing impairment could listen to the digitally processed signals, but not in real time. In 1967, Harry Levitt used BLODI to simulate a hearing aid on a digital computer.
Almost ten years later the second stage began with the creation of the hybrid hearing aid, in which the analog components of a conventional hearing aid consisting of amplifiers, filters and signal limiting were combined with a separate digital programmable component into a conventional hearing aid case. The audio processing remained analog but was able to be controlled by the digital programmable component. The digital component could be programmed by connecting the device to an external computer in the laboratory then disconnected to allow the hybrid device to function as a conventional wearable hearing aid.
The hybrid device was effective from a practical point of view because of the low power consumption and compact size. At that time, low-power analog amplifier technology was well developed in contrast to the available semiconductor chips able to process audio in real time. The combination of high performance analog components for real time audio processing and a separate low power digital programmable component only for controlling the analog signal led to the creation of several low power digital programmable components able to implement different types of control.
A hybrid hearing aid was developed by Etymotic Design. A little later, Mangold and Lane created a programmable multi-channel hybrid hearing aid. Graupe with co-authors developed a digital programmable component that implemented an adaptive noise filter.
The third stage began in the early 1980s by a research group at Central Institute for the Deaf headed up by faculty members at Washington University in St. Louis MO. This group created the first full digital wearable hearing aid. They first conceived a complete, comprehensive full digital hearing aid, then designed and fabricated, miniaturized full digital computer chips using custom digital signal processing chips with low power and very large scale integrated (VLSI) chip technology able to process both the audio signal in real time and the control signals yet able to be powered by a battery and be fully wearable as a full digital wearable hearing aid able to be actually used by individuals with hearing loss.
Engebretson, Morley and Popelka were the inventors of the first full digital hearing aid. Their work resulted in US Patent 4,548,082, “Hearing aids, signal supplying apparatus, systems for compensating hearing deficiencies, and methods” by A Maynard Engebretson, Robert E Morley, Jr. and Gerald R Popelka, filed in 1984 and issued in 1985. This full digital wearable hearing aid also included many additional features now used in all contemporary full digital hearing aids including a bidirectional interface with an external computer, self-calibration, self-adjustment, wide bandwidth, digital programmability, a fitting algorithm based on audibility, internal storage of digital programs, and fully digital multichannel amplitude compression and output limiting. This group created several of these full digital hearing aids and used them for research on hearing impaired people as they wore them in the same manner as conventional hearing aids in real-world situations.
In this first full DHA all stages of sound processing and control were carried out in binary form. The external sound from microphones positioned in an ear module identical to a BTE was first converted into binary code, then digitally processed and digitally controlled in real time, then converted back to an analog signal sent to miniature loudspeakers positioned in the same BTE ear module. These specialized hearing aid chips continued to become smaller, increase in computational ability and require even less power. Now, virtually all commercial hearing aids are fully digital and their digital signal processing capability has significantly increased. Very small and very low power specialized digital hearing aid chips are now used in all hearing aids manufactured world wide. Many additional new features also have been added with various on-board advanced wireless technology (per Wikipedia).
First, a Story:
Three weeks ago I sent my hearing aids in for repair….I’ve heard nothing since.
Second, a Song:
The Hear the World Foundation:
“Founded in 2006 by Sonova, a leading provider of hearing solutions, the Hear the World Foundation supports disadvantaged people with hearing loss around the world and gets involved in hearing loss prevention. The foundation focuses particularly on projects for children with hearing loss, enabling them to develop to their fullest potential. Since its establishment, the non-profit Swiss foundation has supported over 90 projects all around the world with funding, hearing aid technology and expertise. More than 100 high-profile ambassadors, such as Bryan Adams, Bruce Springsteen, Cindy Crawford, Annie Lennox, and Sting support Hear the World as ambassadors for conscious hearing” (per YouTube.com).
The Hear the World Song is by Daniel Cho of Los Angeles, CA and is a Hearing Loss Simulation. I hope you enjoy this!
Thought for the Day:
“The most important thing in communication is hearing what isn’t said.” – Peter Drucker
Have a great day!
Dave & Colleen
© 2021 David J. Bilinsky and Colleen E. Bilinsky
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