Notes

Test audio (speech) signals:
The Open Speech Repository
Harvard Sentences

Praat software tool:
Praat: doing phonetics by computer

More info and diagrams:
Ravindran, G. , Shenbagadevi, S. and Selvam, V. (2010) Cepstral and linear prediction techniques for improving intelligibility and audibility of impaired speech. Journal of Biomedical Science and Engineering, 3, 85-94. doi: 10.4236/jbise.2010.31013.