Apparatus and method are disclosed for the recording of distortion product emission (DPE) levels in human beings. At least one microphone and a sound-delivery system is inserted in the external ear canal in a manner similar to that required to position a small hearing aid. Two primary tones T.sub.f1,...http://www.google.com.tw/patents/US5526819?utm_source=gb-gplus-share專利 US5526819 - Method and apparatus for distortion product emission testing of heating
