Abstract: A hearing aid having a plurality of frequency bands is calibrated by evaluating the response of the hearing aid in each band and programming the hearing aid to produce a specific sound pressure level in each band, thereby providing a calibrated instrument that can be used for both evaluation and compensation of hearing loss. The sound pressure levels are preferably the same for each band. The evaluation step is preferably performed at the center frequency of each band.

Abstract: Data is transferred to and from a hearing aid by transmitting an audible carrier having a frequency greater than 5 kilohertz, modulating the carrier with data, and detecting the modulated carrier in the hearing aid with a narrow band filter. The frequency is in a region where impairment occurs and there are many other sounds, thereby masking the communication, yet not interfering with it.

Abstract: A hearing aid is identified by storing a binary code in the hearing aid, receiving a transmitted code, reading out a subset of bits from the stored binary code, and comparing the transmitted code with the subset for identification. The reading step preferably reads the lowest order nibble, byte, or word of the binary code. In accordance with another aspect of the invention, a charger for the hearing aid, a controller for the hearing aid, and a programmer for the hearing aid store the identification codes for two way communication among the devices.

Abstract: A hearing aid is identified by storing a first binary code in the hearing aid as a first identification code, storing a second binary code in the hearing aid as a default code, and replacing the default code with a second identification code if a second hearing aid is used by the person using the first hearing aid. The identification code includes a bit indicating for which ear the hearing aid is intended. If two hearing aids are used, the identification code of the first hearing aid is substituted for the default code in the second hearing aid and vice-versa, thereby pairing the first hearing aid with the second hearing aid and indicating that there are two hearing aids needed, even if one hearing aid should become lost or inoperative.

Abstract: A hearing aid having a rechargeable battery and a charger for charging the battery includes a first microphone and a first speaker in the hearing aid and a second microphone and a second speaker in the charger for acoustically transferring data between the hearing aid and the charger. The hearing aid can detect the charge state of a battery and send a signal to the charger indicative of the charge state. The charger also includes a chamber for receiving at least a portion of the hearing aid.

Abstract: A microcontroller having digital to frequency converter and pulse frequency modulator capabilities. The digital to frequency converter (DFC) generates a 50 percent duty cycle square wave signal that may be varied in frequency, wherein the 50 percent duty cycle square wave signal is directly proportional and linear with a count value put into an increment register. The pulse to frequency modulator (PFM) generates pulses having pulse widths of the input clock for each rollover of a counter. The frequency of these pulses is directly proportional and linear with the count value put into the increment register.