A hearing aid typically comprise an ear mold or housing in which the necessary electronics for amplifying and otherwise conditioning sound to compensate for a user's hearing loss. Such electronics generally include a microphone for receiving the sound and converting the sound to an electrical signal, an integrated circuit (IC) or speech signal processor for amplifying and processing the signal produced by the microphone, a speaker, also known as a receiver, for converting the processed signals into sound energy and a battery for providing operational power to the hearing aid. The ear mold can be generally made of plastic, and is specially designed and molded to fill the ear of the person who is to use the hearing aid. Electroacoustic miniature transducers are employed for converting electrical signals into acoustic signals as well as for converting acoustic signals into electrical signals. Once a speech processor processes ambient acoustic signal, the altered signal is provided to an implanted transducer that stimulates the hearing impaired person's auditory system. The auditory stimulation may be done acoustically, mechanically, or electrically as a function of the type and severity of the hearing loss in the hearing impaired individual. Most hearing aids include an acoustic sensor (i.e. a microphone) as well as a magnetic sensor (i.e. a telecoil). Telecoils are inductive devices which are used to receive signals that are not acoustic in origin. The acoustic sensor is used as the principal sensor for sensing an input acoustic signal that contains acoustic information which may comprise audio information (i.e. speech, music or other important sounds such as alarms, warnings, etc.). The magnetic sensor is an alternate sensor that is used in certain situations for sensing an input magnetic signal that contains magnetic information that is in many instances similar to the audio information. By the use of a simple switch, the hearing aid wearer is able to activate the telecoils and deactivate the microphone, thereby eliminating problems of feedback, distortion and background noise. Hearing aids often include a connector with a set of closely spaced electrical terminals operatively connected to one or more internal hearing aid components. Such connectors normally form part of the housing of the hearing aid and may be located at the outer surface or at least near the outer surface. Normally, the connector in a hearing aid comprises two or more electrical terminals which are connected to internal hearing aid components. The switching or control of hearing aids usually ensues with switches, keys or controls at the housing of the hearing aid device. Hearing aids typically contain a battery that powers electrical circuits that amplify sound. To conserve power the hearing aid may have an on/off switch that allows a user to disconnect the battery from the circuits.

Numerous types of hearing aids are known and have been developed to assist individuals with hearing loss. Hearing aids are normally divided into three categories: behind the ear (BTE) aids, in the ear (ITE) aids, in the canal (ITC) aids, or completely in the canal (CIC) aids. From the purely technical point of view, such hearing aids can be configured as so-called analog aids, as digital aids, or as aids with a combination of analog and digital techniques. In-the-ear (ITE), in-the-canal (ITC) and completely-in-the-canal (CIC) hearing aids generally have similar topologies and are differentiated by their respective sizes. The ITE type is subdivided further according to the depths of insertion and sizes. These hearing aids typically include a receiver, a microphone, a replaceable battery and amplification electronics contained within a semi-rigid housing. To prevent acoustical feedback, the hearing aids can also include a compliant acoustical sealing element that includes the space between a hearing aid and an ear canal. ITE hearing aids are generally larger than ITC units which are generally larger than CIC hearing aids. BTE hearing aids worn behind the ear are commonly constructed of two housing shells in which separating walls form multiple separate chambers within the interior of the housing. The behind-the-ear (BTE) aid is quite visible to third parties. Such BTE hearing aids also generally do not perform well in noisy environments. In-the-ear (ITE) hearing aid solutions that are less visible and also provide improved performance in noisy environments have therefore been developed using directional microphone technology. However, that ITE hearing aids as such are less visible and provide substantial improvement in directivity performance, ITE hearing aids still require that the entire concha of the wearer's ear be filled, and that the directional microphone be located on the near flat outer surface of the hearing aid. This arrangement is still quite visible. Consequently, less visible hearing aids have been developed for in the ear applications, namely in the canal (ITC) and completely in the canal (CIC) hearing aids. ITC and CIC hearing aids are discreetly located in the resonant portion of the ear canal, and thus do not require that the entire concha of the ear be filled. Hearing aid wearers generally prefer the less visible ITC and CIC hearing aids over ITE hearing aids. ITC and CIC hearing aids, however, do not perform as well as ITE hearing aids, or even BTE hearing aids, in noisy environments.

Hearing aids for rehabilitating damaged inner ear typically pick up sound with a microphone and using this microphone, convert the sound into an electrical signal. Hearing aids that have the capabilities of a directional microphone and an omni-directional microphone are advantageous to the user. In certain situations an omni-directional microphone is preferred to a directional microphone and vice versa. Some hearing aids use adaptive microphone matching systems to balance long term characteristics of a pair of omni-directional microphones. In a directional hearing aid with an adaptive analogue matching circuit which controls the gain of an adjustable preamplifier in an input signal channel, the value of the gain is derived from a measured difference in average output signal level between the input signal channels. Hearing aids having a directional sound receiving characteristic are useful to improve speech perception in noisy environments, where sound signals may be received simultaneously from different directions, as is the case e.g. in the noise environment frequently referred to as cocktail party noise. On the other hand, in environments with only a low noise level or no significant speech signals the hearing aid user will normally prefer an omnidirectional or spherical sound receiving characteristic, offering the same perception of sound irrespective of the direction. In addition to one or more microphones, induction receivers which permit a hearing coil mode are provided in hearing devices. This ensures that acoustic signals are transmitted inductively to the hearing device by a telephone device which has an inductively operating loudspeaker. Hearing aids can provide adjustable operational modes or characteristics that improve the performance of the hearing aid for a specific person or in a specific environment. Some of the operational characteristics are volume control, tone control, and selective signal input. One way to control these characteristics is by a manually engagable switch on the hearing aid. The switching or control of hearing aids usually ensues with switches, keys or controls at the housing of the hearing aid device. Conventional hearing aids are analog or digital devices which filter and amplify sound. The frequency response of the filter can be configured to compensate for the frequency-dependent hearing loss of particular users. More sophisticated hearing aids can compress the dynamic range of detected sounds amplifying softer sounds below the threshold of hearing while maintaining loud sounds at their usual levels so that they do not exceed the threshold of discomfort. In digital hearing aids, the signal processing unit is correspondingly digital and comprises an input-side analog/digital converter and as called for an output-side digital/analog converter.

Hearing aids of various function and features can satisfy different degree of hearing deficiency. Hearing aids can be programmed to make response to micro-sound, so as to transmit more clear and melodious sound to make the user better understanding. Hearing aids are usually able to respond to the different auditory situations because the hearing aid user can switch them into different hearing programs. Modern hearing devices are usually capable of coping with different hearing situations by being able to be switched into different hearing programs by the wearer of the hearing aid. A typical hearing program is the telephone hearing program in which acoustic signals which are picked up by the microphone of the hearing device are filtered in accordance with the frequency spectrum of telephone signals in order to suppress disruptive ambient noises in other spectral ranges. With the advent of programmable hearing instruments, it has become possible to achieve near optimal matching between the electroacoustic responses and the targets. Programmable hearing aids are programmed by connecting them to a programming unit. In order to program a hearing aid the connector includes at least one electrical terminal adapted to form a data communication path between the external device and one or more internal components of the hearing aid during programming. The hearing aid may be supplied with setting data from the external programming device connected thereto, or the hearing aid may exchange data with the programming device. Programmable hearing aids offer the possibility of making choices for the values of multiple parameters, hence allowing for a very wide range of electroacoustic responses capable of accommodating many different kinds of hearing impairments.