A signal frequency analyzer and frequency response shaping apparatus using digital techniques and apparatus and methods using the same which is applicable, in one embodiment thereof, to the enhancement of hearing in hearing impaired persons. Analog techniques are used in another embodiment of the invention....http://www.google.com.tw/patents/US5663727?utm_source=gb-gplus-share專利 US5663727 - Frequency response analyzer and shaping apparatus and digital hearing enhancement apparatus and method utilizing the same
