Lots of theoretical battles about exactly how to represent this prominence. The higher pitch seems to be the most important cue to the listeners in English. Each syllable in English words is marked for being stressed or unstressed. By marked , I mean that the dictionary entry for the Lexicon is another word for dictionary . Because of a second phenomenon called accent or pitch accent Pitch Accent Stress is a fact about words.
Pitch accent is a fact about utterances or pieces of utterances called intonation phrases .
It depends on the rate of vibration of the vocal cords. Higher pitch, higher frequency of vibration than in sound with lower pitch. Each opening and closing of vocal cords causes a peak of air pressure in the sound wave, estimate the pitch of a sound by counting rate of occurrence of peaks. Generally pitch accents can only happen on a syllable that is lexically allowed to have stress.