TODAY’S PATENT – HEARING AIDS
This was invented by the joint work of Roger F. Laurence & Leon R. Morgan which was granted patent bearing the patent grant number. US4996712A on 26th February 1991, later being assigned to Etymotic Research Inc. On 30th June 1995.
The current invention relates to hearing aids, and more specifically, to a hearing aid for people with moderate to severe hearing loss that transmits acoustic signals at a substantially constant average signal level. The invention “hearing aid” consist with automatic gain control that produces an average output signal level that is essentially constant.
In order to accommodate impulsive sounds or transient signals, the automatic gain control arrangement has two control generators: a slow control generator that provides a relatively slow release time and adjusts the gain to the average level of the input signal, and a fast generator that provides a relatively fast release time. The fast generator controls the gain when a loud enough impulsive sound is heard in order to prevent discomfort or overloading. The dynamic range for sound pressure levels above a threshold, such as 60 dB SPL, is constrained by the automatic gain control arrangement.