If I order a 100% digital hearing aid, is that available as a class D, or are those 2 things mutually exclusive?
The two are really mutually exclusive. When you order an instrument that is ''100% digital,'' you receive an instrument that has a digital amplifier. A Class D circuit would not be necessary in most cases.
With a digital hearing instrument, the analog signal (sound hitting the microphone) is converted into a digital format by the analog-to-digital (A/D) converter and amplified within that format before being converted back to an analog signal. Other manipulations of the signal can also occur in the digital signal processing (DSP) format such as acoustic feedback reduction, noise reduction, and control of the directional microphones. When the term ''100% digital'' is used, it can be misleading as the majority of current ''digital'' hearing instruments still have some analog components such as the microphone and receiver (speaker). Rather, this term is intended to mean that the hearing instrument has the capability to amplify within a digital format. The term ''digitally programmable'' can apply to both analog and digital instruments. ''Digitally programmable'' instruments that use analog amplifiers are programmed via a computer or hand-held programmer to set the controls of the instrument; however, once programmed they are analog amplifiers. In other words, they do not employ any digital signal processing.
Angela Pool has been an Educational Specialist and trainer with Siemens Hearing Instruments for the last four years. Prior to joining Siemens she worked as a clinical audiologist at Mayo Clinic and the University of Florida Pediatric Hearing Program. Ms. Pool received her Masters degree in Audiology from the University of South Alabama.
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