Introduction to Hearing Aids is a good introduction to technology inside hearing aids. The two basic types of technology for hearing aids are analog and digital. Analog hearing aids process electrical sound in the analog domain; the more recent digital hearing aids process electrical sound in the digital domain. The earliest analog hearing aids simply amplified both speech and noise, and were ordered after testing to determine the particular frequency response needed by the patient. Newer analog hearing aids can be programmed during the fitting process and can have multiple listening profiles. Digital hearing aids are also programmable during the fitting process and have multiple listening profiles that are selectable by the patient. The vast majority of hearing aids sold today are digital because of their increased performance and flexibility over the analog versions. Some hearing aids are beginning to use rechargeable single-cell lithium-ion (Li+) batteries, but most hearing aids are still powered by primary zinc-air batteries.
Introduction to Hearing Aids and Important Design Considerations application note introduces the styles of hearing aids, including behind the ear (BTE), in the ear (ITE), in the canal (ITC), and completely in the canal (CIC), as well as a brief summary of both analog and digital hearing aid technologies. Also discussed is the importance of the audio-processing path, the functions of electrical components, and some critical elements that designers must consider when selecting products.