A vocoder device and corresponding method characterizes and reconstructs speech excitation. An excitation analysis portion performs a cyclic excitation transformation process on a target excitation segment by rotating a peak amplitude to a beginning buffer location. The excitation phase...http://www.google.ca/patents/US5794186?utm_source=gb-gplus-sharePatent US5794186 - Method and apparatus for encoding speech excitation waveforms through analysis of derivative discontinues 
