With the improvement of people’s living standards and the popularization of health awareness, the incidence of conductive hearing loss has been declining globally year by year, and the development of otology has enabled the vast majority of conductive hearing loss to be cured through medication or surgery, and hearing preserved or improved to a certain extent. However, for patients with sensorineural hearing loss, there is no clear and reliable medication or surgical treatment that can cure them, and they can only rely on hearing aids such as hearing aids and cochlear implants to help hearing impaired people realize hearing compensation or reconstruction.
Hearing aids are small amplification devices that compensate for the hearing loss of hearing-impaired patients and are relatively economical and widely used hearing aids. The development of hearing aids is a process of applying new technologies to meet the ever-increasing hearing requirements of hearing impaired patients. The development of hearing aids can be categorized into the following five eras: the primitive sound collection era, the charcoal element era, the vacuum tube era, the transistor and integrated circuit era, and the digital hearing aid era.
Proto-Collective Voice Era
Looking back at the history of hearing aids, in ancient times, if people were hard of hearing, the only thing they could do was to simply cup one of their hands and hold it behind their ear to amplify the sound. The original appearance of hearing aids was inspired by this way of collecting sound in the palm of the hand, and there were “ear trumpets” like horns or conchs, wooden “hearing boards” and “hearing tubes”, “hearing caps” like hats and bottles, and “hearing caps” like a bottle. like hats and bottles; “ear flaps” like animal wings; and very long (up to tens of centimeters, or even more than a meter long) stethoscope-like “speech tubes”. “Speech tubes”. These simple mechanical hearing aids were used for hundreds of years until the 19th century, when they were gradually replaced by carbon-based hearing aids.
Charcoal Elemental Era
The first telephone-type hearing aid was patented in 1892. It was a charcoal hearing aid using the principle of electrical amplification, powered by a battery, and consisting of a charcoal microphone and a magnetic headset. Because the gain of the carbon hearing aid is small, while the noise is large, the distortion is more, and the carbon is susceptible to humidity, so the use of a relatively short period of time, it was replaced by the vacuum tube hearing aid.
vacuum tube era
The vacuum tube hearing aid was introduced in 1907 and the first tube hearing aid was produced in England in 1921. It offered greater gain and better clarity. The first tube hearing aids were large and required heavy batteries, making them almost impossible to use on the go. Over time, tubes and batteries became smaller and smaller, and the miniaturization of tubes in 1938 was a turning point in the history of hearing aids. The advent of the mercury cell made it possible to significantly reduce the size of hearing aids, and batteries and hearing aids could finally be combined into one. At the same time, small crystalline earphones were introduced, which made it possible to manufacture portable hearing aids in cassettes.
Transistor and integrated circuit era
Due to the various new technologies and materials that emerged during World War II, integrated hearing aids became significantly smaller. During this period, semiconductor spectacle hearing aids and spectacle hearing aids appeared. the introduction of transistors in the 1950s replaced the electronic tubes, making the hearing aids smaller in appearance, less likely to break, and with a longer service life.
In 1964, the introduction of integrated circuits hearing aids, with a smaller size, lower power consumption, better stability. Integrated circuits have revolutionized electronic products. At the same time, with the development of integrated circuits, the shape of the hearing aid also has a variety of changes. From the hairpin and eyeglass styles of the earliest transistor days, to the behind-the-ear styles of the integrated circuit days, followed by the ear canal styles of the 1980’s, and then to the 1990’s, when the birth of the full ear canal styles made hearing aids nearly invisible in appearance.
The age of digital hearing aids
In the mid to late 1980s, Digital Signal Processing (DSP) chips began to be used, and hearing aids entered the era of “programmable” hearing aids.DSP chips have the functions of storage and operation: on the one hand, they store hearing data and various parameters determined after selection; on the other hand, they can dynamically analyze the differences in the external input signals and determine the working process of other analog components in the circuit. On the other hand, it can dynamically analyze the differences in external input signals and determine the working process of other analog components in the circuit.
In the mid-1990s, digital signal processing chips became more powerful and smaller, and in 1996, Widex and Oticon launched the Senso and Digifocus almost simultaneously, the first fully digital hearing aids. In addition to the tiny size (such as the CIC can be completely placed in the ear canal), or hardware-based dedicated DSP closed platform, fully realized with digital circuit hardware. The software is fully embedded in the hardware circuitry and there are no redundancies in the structure, resulting in high processing speeds (tens of millions of operations in 1s without perceived latency).
Today’s hearing aids use tiny chips, completely replacing the huge bodies of 100 years ago. Advances in technology have not only changed the quality, but also manifested in the continuous breakthroughs in appearance and design. From tube hearing aids, vacuum tube hearing aids, integrated hearing aids, transistor hearing aids, programmable hearing aids, to today’s all-digital hearing aids, hearing aids are getting smaller and more fashionable. At the same time, most of the common all-digital hearing aids nowadays use a special DSP chip, with an operation speed of about 100 million times per second or more. The use of digital technology, low noise, small distortion characteristics, the development of a number of human ear hearing perception model based on the “artificial intelligence” processor, and in the selection method put forward a new concept.
Mr. Ernst, President of the European Hearing Aid Industry Association, stated in 2006: “As we all know, the hearing aids of yesteryear are no longer the same as today’s complex hearing systems, except for the name”. Today’s hearing systems are not only vastly different from traditional hearing aids in terms of hardware, but more importantly, a breakthrough in terms of their functionality and range of use, with the power of software revolutionizing the reinvention of the hearing aid.
The following section describes the main hearing aid technologies currently available.
● In-situ audiometry in the real ear: This refers to the actual hearing threshold test after the patient has been fitted with a hearing aid. In pure tone audiometry, headphones are often used, which does not take into account the effects of the blockage of the external ear canal and the position of the transmitter after the actual wearing of hearing aids, which may cause a difference in the hearing threshold after the actual wearing of hearing aids. Therefore, after the real ear in situ audiometry, the actual hearing threshold after wearing hearing aids can be accurately obtained, so that the subsequent commissioning of hearing aids can be more accurate.
● High-precision localization system: an upgraded version of directional technology. Improving speech resolution in noisy environments has always been one of the goals in the development of hearing aid technology in the process of hearing aid fitting, so the use of directional microphone technology in the field of hearing aids has always been a concern, and it is the only hearing aid technology that has been proven time and time again to be able to contribute to the improvement of the signal-to-noise ratio of hearing aids, and to help hearing aid wearers improve their speech recognition rate. The high-precision localization system is an enhancement of the traditional directional technology, which is able to differentiate the noise position of each frequency band in real time and make directional changes in real time, so as to more effectively improve the overall signal-to-noise ratio in a noisy environment, as well as to realize easy listening to the sound in the rear.
● Noise Reduction – SII Speech Enhancement: Noise reduction is a technology that distinguishes and removes noise from signals with noisy speech. In the field of hearing aids, the question of how to make hearing aids process sound better in noisy environments, thereby helping hearing aid users to obtain clearer speech signals, has always been a concern for audiology clinicians and hearing aid users. This is because high-quality noise reduction is one of the most important reasons for hearing aid wearers to accept and use hearing aids more easily, and also because the biggest problem for hearing aid users is the understanding of speech in various noise environments. The traditional noise reduction method is to reduce the gain compensation of the hearing aid in the noise environment, but the reduction may also affect the pickup of speech. Therefore, a new computational method of compensating itself by calculating the speech intelligibility index (SII) is now emerging based on the traditional noise reduction method. The designers of this noise reduction method call it speech enhancement (SII), and SII uses different gain reductions for users with different degrees of hearing loss to help users with all types of hearing loss obtain optimal speech intelligibility, thus further enhancing their speech intelligibility.
● Frequency shifting technology: This refers to the transfer of important high-frequency speech signals that cannot be heard by hearing aid wearers without high-frequency residual hearing or with poor high-frequency residual hearing to the low and mid-frequency bands in which they still have good residual hearing. Current hearing aid frequency shifting technology can be broadly categorized into linear frequency shifting technology and non-linear compression frequency shifting technology according to different signal compression processing modes. Linear frequency shifting technology, i.e. hearing extension technology, is a linear frequency shifting hearing aid technology, which mainly moves the high-frequency sound without high-frequency residual hearing or with poor high-frequency residual hearing linearly to the low and mid-frequency regions where there is still a certain degree of residual hearing. Non-linear compression frequency shifting is a technique that compresses high-frequency sounds with no or poor high-frequency residual hearing into neighboring lower-frequency regions by means of frequency compression.
● Intelligent Wind Noise Processing Technology: In windy environments, the wind creates a vortex at the hearing aid microphone, which directly impacts the microphone, causing the hearing aid wearer to feel a louder impact noise than the actual wind sound. The impact of wind noise is a problem that the hearing aid industry is constantly exploring solutions to. Currently, the common solution is to reduce the low-frequency gain and change the directionality of the hearing aid to omnidirectional, so as to improve the impact of wind noise. Or use sound intertransmission technology to transmit the sound from the side with high signal-to-noise ratio to the side with low signal-to-noise ratio, but this requires binaural hearing aids and different binaural signal-to-noise ratios, limiting the effect of wind noise reduction. Meanwhile, there is also a new intelligent wind noise processing technology, which detects speech sound or wind noise through dual microphones detecting wind noise separately, and distinguishes the correlation of the microphone input signals by a classifier, so as to realize the improvement of signal-to-noise ratio in wind noise environments. It provides users with better speech recognition in wind noise environments, and enables smooth and clear listening, whether worn in one ear or riding into the wind.
● Sound Classification Technology: It means that hearing aids are able to make automatic functional adjustments in different environments, reducing the need for hearing aid users to switch between programs for different environments, and smarter sound processing so that hearing aid wearers can better adapt to hearing aids and all types of different environments.
● Tinnitus treatment program: The incidence of tinnitus is increasing, with an average of 3 tinnitus patients in every 20 people. Tinnitus treatment methods include acoustic therapy, masking therapy and habituation therapy, and many hearing aid manufacturers have added tinnitus masking or habituation methods to their hearing aids, and even have specialized tinnitus treatment programs to help address the impact of tinnitus on users.
● MFi wireless direct connection technology: MFi means that the hearing aid is able to transmit the signals (including voice signals such as phone calls and audio signals such as music and video) from the iPhone directly to the hearing aid through the low-power 2.4G Bluetooth transmission technology, without the need to pass through any other auxiliary equipment; at the same time, the hearing aid wearer can also make personalized adjustments to the sound through the cell phone APP, so as to realize the convenience, personalization and intelligence.
● Rechargeable technology: the hearing aid is rechargeable.Rechargeable technology: Hearing aid wearers don’t need to worry about replacing batteries, which can be recharged directly through the charging cradle, just like a cell phone. Currently, rechargeable batteries can be fully charged in 3 to 4 hours for all-day use without worrying about running out of power. In the future, fuel cells that can be recharged in less than 10 seconds will also be available. At the same time, there will also be hearing aids with 2.4 GHz wireless direct and rechargeable functions, which will give hearing aid wearers more advanced, intelligent and convenient options.
The Future of Hearing Aids
In the future, hearing aids will be either assistive listening devices or fashionable digital gadgets. Fashion, convenience and high technology will gradually become the definitive words to put in front of hearing aids.
