Another aspect of acoustic phonetics is the analysis of the suprasegmental features of speech. When we hear the tones of a tone language, or the intonation of an utterance, we experience the sensation of pitch. This only happens in the case of voiced sounds. The sensation of pitch is related to the frequency of vocal fold vibration, which we call fundamental frequency. This means that we have one word (pitch) for a subjective sensation and another (fundamental frequency, or F0) for something that we can measure objectively. In a similar way, we can perceive the loudness of a sound or syllable, and we can also use instruments to measure its intensity; we perceive the length of a sound, and can measure its duration. Using computers to measure fundamental frequency and duration, we can discover a lot about such aspects of speech as intonation, stress and rhythm.