Prof. Andrea Angelini discusses the concept of timbre, or tone quality, in singing voices. Timbre is determined by the harmonic content and dynamic characteristics of a sound. The resonances of the vocal tract, including the pharynx, mouth, and nasal cavities, change the spectrum produced by the vocal cords by amplifying certain harmonic frequencies called formants. The first formant allows distinction between vowels and enables speech. Timbre also differs among singing registers and voice types due to variations in resonance. The "singing formant" around 3000 Hz further distinguishes voices from classical instruments.