Hearing aid in ear. A multi-channel hearing aid in a man's ear. The plastic flap is the lid of the battery case. Hearing aids are fine-tuned to amp- lify the particular range of frequencies needed by each patient. This hearing aid gives even finer control by dividing incoming sound into multiple channels, and amplifying each channel according to the patient's needs. Hearing aids improve hearing in people with partial deafness. Sound is picked up by a tiny microphone, amplified, and then transmitted into the ear by a tiny speaker.