Every phoneme can be completely and uniquely described by using the acoustic-phonetic descriptors.

Time varying nature of the excitation source can be clearly observed from the speech waveform.

a. Quasiperiodic waveform during voiced speech

b. Random noise-like waveform during unvoiced speech

c. Lack of any significant signal amplitude during silence or nonspeech region

d. Low or negligible signal amplitude (closure region) followed by a burst during the production of plosive sounds.