Stops and Aspiration
Stops appear on the spectrogram as a brief cessation of noise caused by the closure of the articulators, followed by a burst of energy as the articulators come apart. For aspirated stops, there will also be a short bit of random energy visible on the spectrogram due to the aspiration.
On the spectrogram
below of the sentence "Tell me a story" there are two instances of the phoneme
/t/: [th] in "tell" and [t] in "story". The relevant features have
been marked below on the spectrogram. Note that the burst energies of the two
sounds are very similar, since they are produced at the same place of articulation.