Digital signal processing (DSP) allows manufacturers to equip today's hearing aids with many 'smart' features to improve your hearing experience. The features your hearing professional recommends for you will depend upon the specifics of your hearing loss as well as your lifestyle needs.
Digital processors actually convert sound into a string of numbers, which can be specifically manipulated (for example, annoying low-level environmental sounds can be compressed while important sounds like speech can be expanded)*. Because digital hearing aids can be programmed to suit individual hearing loss types and personal preferences, they are far more likely to satisfy the wearer than analog hearing aids.
- DSP is intelligent. It enables the identification and classification of sounds from the environment (such as speech, music or noise).
- DSP is flexible. Algorithms can be programmed to reduce noise and amplify meaningful sounds according to the needs of the wearer,
- DSP is precise. Hearing aids can be programmed to amplify not ust speech, but specific parts of the speech spectrum such as the high-frequency consonant sounds "sh" and "t".
Your hearing professional may also be able to use digital hearing aid features and fitting software to perform a more accurate fitting, as well as to verify sound levels through the hearing aids when you pick them up.
Top Digital Hearing Aid Features
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Smart and automatic: Digital signal processing
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Digital signal processing is the analysis of an incoming signal and the classification of that 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.
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More customization: Channels and bands
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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 amplified where necessary according to the programmed settings for the specific hearing loss.
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 can't hear—like a "graphic equalizer" in music recording and playback
The majority of today's hearing aids have multiple channels. A minimum of four channels in a hearing aid is recommended and 16 is optimal. Multiple channels are also useful for implementing other features such as digital noise reduction and feedback cancellation.
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Not too loud: Automatic gain control-output
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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.
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Not too soft: Automatic gain control-input
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This feature is also used to "repackage" speech signals (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 like p,s,or k —and then occur automatically.
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Keeps the noise out: Digital noise reduction
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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 speech.
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No squealing: Feedback cancellation
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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.
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Volume where you need it: Directional microphone technology
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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.
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Automatic sound tracking
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Some hearing aids automatically switch to a directional mode to track speech or provide maximum reduction in volume if the sound source is "noise."
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Multiple memories
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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.
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Discreet controls
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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 smart phone.
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Talking on the telephone
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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 size limitations.
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Telecoils and "Loop Systems"
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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 permanent wire that surrounds an audience.
* Ricketts, T. (2011) Digital hearing Aids: Current “State-of-the-Art.” American Speech-Language-Hearing Association, www.asha.org
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