Digital Hearing Aids
Digital hearing aids boast today’s most advanced technology.
Digital hearing aids are programmable hearing instruments with digital circuits. These digital circuits are more flexible than analog circuits. The analog circuits increased the volume of all incoming sounds and sometimes made loud sounds too loud and soft sounds too soft. These types of circuits were also prone to feedback (whistling noise) and distortion. Digital circuits can be precisely programmed to match the patient’s individual hearing loss, sometimes at each specific frequency/pitch. Digital circuits offer improved clarity of sound, less circuit noise, faster processing of sound, and improved listening in noise when compared to analog circuits. Digital hearing aids are easy to use because they adjust volume automatically.
Digital hearing aids represent the most advanced technology available today allowing the most precise prescriptive fitting available. Older analog hearing aids turned everything up, but digital hearing aids focus on clarity and comfort through sophisticated control of the sound signal inside the hearing aid.
If you think about the sounds that you can hear and sounds that you cannot hear, these sounds differ in pitch (ex. keys on a piano) and they differ in volume/loudness. Digital processing can shape your amplification (volume and clarity of signal which you hear through the aid) by changing pitches and changing volumes.
Digital hearing aids also offer many other feature like directional microphones and multiple programmable memories to enhance the user’s benefit in different listening environments. The key is the tiny computer chip that manipulates the incoming soundwaves according to logic principles supplied by the various manufacturers. The modern digital hearing aid can provide a hearing-impaired person with an improved and more pleasant sound picture, but it cannot bring back normal hearing. Even digital hearing aids are limited by many factors of hearing loss such as speech understanding abilities, extent of damage to the inner ear and entire auditory pathway. Like many other high-tech devices, high expectations can accompany digital hearing aid devices. Counseling patients as to the realistic expectations of digital amplification will continue to be most important, but the future looks bright as technology and processing schemes continue to improve.
How Digital Hearing Aids Work
In a very rough sense, the digital hearing aid has five major components: the microphone, the analog to digital converter, the core, the digital to analog converter, and the receiver. Sound waves hit the hearing instrument microphone where they are converted to an electrical signal (analog).
The signal then passes through an Analog to Digital converter (A/D converter) where it is changed to a sequence of 1s and 0s. This sequence is sent to the “core” where it is filtered into bands and channels, then manipulated according to the programmed settings for the specific hearing loss. Each hearing aid manufacturer may have its own proprietary set of rules that it applies to the digital speech envelope. The manipulated signal is then channeled through a Digital to Analog converter (D/A) where the end result is an analog signal that has been manipulated according to the hearing loss and proprietary chip logic. This signal then travels to the receiver where it is converted back to an acoustic signal that the user then hears. In other words, the digital hearing aid has a tiny computer chip in it that can manipulate the sound according to specific frequency (pitch) and specific volume level to deliver a clear sound set precisely to the user’s hearing loss.
The dispenser or audiologist then has the ability to manipulate many aspects of the digital processor, like gain, compression (control the loudness of sounds), and acoustical feedback (whistling noise) through the computer interface. The result is a more precisely fit hearing instrument and a happier hearing aid user.