Hearing Aid Technology
Within these various hearing aid styles, there is a range of technology features that can be used to manage and amplify sound. Today's hearing instruments offer many kinds of advanced programmable and digital processing features to enhance the listening experience in different environments. Your hearing professional will demonstrate the various styles and explain the technology features available, recommending the combination that best suits your hearing needs and lifestyle. Read more about digital hearing aid technology below.
Smart and automatic: Digital signal processing
Digital signal processing describes the analysis of an incoming signal and the classification of the sound as speech, noise, music or feedback, for example. Digital signal processing triggers automatic activation of other special features—such as noise cancellation, feedback cancellation, or voice amplification.
More customization: Channels and bands
Channels and bands are components of sound. Digital hearing aids convert analog sound to digital sound and send the digital "data" to the processor where it is filtered into bands and channels, then changed according to the programmed settings for the specific hearing loss.
The majority of today's hearing aids have multiple channels. Each channel represents a portion of the frequency range important for understanding speech. One advantage of multiple channels is that features such as gain control (adding volume to sound) and compression (decreasing the volume of sound) can be programmed differently to compensate for the wearer's hearing across different frequencies.
For example, if you can hear low-pitched sounds well, but not high-pitched sounds, digital hearing aids can be programmed to amplify just the sounds you don't hear—like a "graphic equalizer" in music recording and playback. Unique bands of sound are individually controlled to optimize sounds in the speech spectrum.
Multiple channels are also useful for implementing other features such as digital noise reduction and feedback cancellation. The channels in a hearing aid are similar to the channels of a graphic equalizer. At certain pitches or frequencies, volume can be increased or decreased depending on the hearing aid wearer's needs. A minimum of four channels in a hearing aid is recommended and 16 is optimal.
Not too loud: Automatic gain control-output
Automatic Gain Control-Output is the digital signal processing feature that puts a ceiling on loud sounds to ensure that sounds remain at or below the comfort threshold in the hearing aid.
Not too soft: Automatic gain control-input
Automatic Gain Control-Input is the name of the feature used to "repackage" the speech signal (and other incoming sounds) to increase the volume of soft sounds. The beauty of digital signal processing is that these amplifications can be programmed for specific frequencies of speech sounds—such as consonant sounds—and then occur automatically.
Keeps the noise out: Digital noise reduction
Digital noise reduction analyzes the sound input and differentiates speech from noise signals. Digital noise reduction is accomplished simultaneously in multiple channels to reduce the sound of noise. Digital noise reduction addresses one of the biggest complaints of hearing aid wearers by reducing noises that interfere with the sounds of interest—such as speech.
No squealing: Feedback cancellation
Feedback cancellation is the automatic feature that detects and cancels whistling or squealing before it happens. Acoustic feedback is the whistling sound caused when something gets too close to the microphone on a hearing aid or when the hearing aid is improperly fitted. Feedback cancellation addresses the other chief complaint of hearing aid wearers by canceling whistling before it happens.
Volume where you need it: Directional microphone technology
Directional microphone technology is designed to increase the volume of sounds (such as speech) coming from the front of the hearing aid user and decrease background and side noise. Directional technology is available on all hearing aid styles except completely-in-canal (CIC) hearing aids because of size constraints.
Automatic sound tracking
Some hearing aids automatically switch to a directional mode to track speech or provide maximum reduction in volume if the sound source is "noise."
A memory is a location on the digital processor where hearing aid settings can be recorded and stored for multiple listening situations. It is common for hearing aids to have up to four memories. In a hearing aid with three memories, one memory location will be programmed for listening in quiet, a second memory location will be for listening in noise, and the third will be for use with the telephone.
To alternate between memories on a hearing aid, the user touches a button on the aid or uses a remote control device. In some digital hearing aids, memory switching is automatic. Advanced features, like multiple memories to control hearing across a range of bands and channels, do add cost to hearing aids but also increase effectiveness in a variety of settings.
Remote controls are ideal for very small digital hearing aids where controls on the hearing aid would be too small for manual adjustment. Remote controls can fit in a pocket, appear as a feature on your watch or as an application on a smartphone.
Talking on the telephone
A telecoil is a special circuit that picks up electromagnetic signals from the handset of the telephone and amplifies them in a manner similar to the amplifying function of the hearing aid.
Often, hearing aids with multiple memories will devote one memory to the telecoil. In these instruments, the telecoil can be accessed through a push button on the hearing aid or by the use of a remote control device. In analog hearing aids, the telecoil was problematic because the hearing aid microphone remained open when talking on the phone—sometimes causing feedback. In digital hearing aids, the microphone and telecoil operate independently so phone volume can be increased without causing acoustic feedback.
Telecoils are not available in some smaller custom-made models due to space limitations.
Telecoils and "Loop Systems"
Telecoils (also called T-coils) are often compatible with loop systems such as those used in theaters and churches to amplify the sound of the performer or speaker directly to hearing-aid wearers. Loop systems transmit sound magnetically from a microphone to telecoil-equipped hearing aids through a wire that surrounds an audience.