How are diphthongs characterized in phonetics?

Diphthongs are characterized in phonetics as a smooth transition between two vowel sounds. This means that when a diphthong is produced, the speaker starts at one vowel sound and glides into another within the same syllable. This blending creates a single, complex vowel sound that differs from a simple vowel, where the sound remains steady without any transition. The movement between the two vowel qualities is what defines a diphthong, making it particularly distinctive in spoken language. Recognizing this characteristic helps in understanding how certain vowel combinations function in speech, contributing to pronunciation and accent variation.