Image Number 2 for United States Patent #5832097.
A multi-channel synchronous compander for hearing aids, in which the input signal from an input transducer is directed through a 2:1 front compressor, then through a band splitting filter to divide it into a desired number of frequency bands, then through expander/compressors to provide selected expansion/compression of each frequency band depending on the user's hearing impairment. The outputs of the expander/compressors are summed, amplified and directed to the hearing aid output transducer. The compressor and each expander/compressor are all controlled by control signals derived from the compressed signal level at the output of the front compressor. The use of common control signals for both the front end compression and the expansion removes the need for close matching of temporal performance and improves the output signal fidelity. The front compressor allows the filter capacitors to be reduced in size so that they can be integrated. Sounds above a high level threshold do not change the gain applied to input signal, even when changes are made in the expansion/compression ratios of the expander/compressors.