L.R. Rabiner and R.W. Schafer, Digital Processing of Speech Signals, Chapter 4, New Delhi, India : Pearson Education Inc., 1993.

L.R. Rabiner, Biing-Hwang Juang and B. Yegnanarayana, Fundamentals of Speech Recognition, Chapters 2 and 3, New Delhi, India (Indian Subcontinent Adaptation) : Pearson Education Inc., 2009.