The human voice and most natural sounds are complex and contain a mix of frequencies and amplitudes. When you produce different vowels and sounds, you are manipulating the characteristics of the sound waves in various ways. This manipulation involves changes in the fundamental frequency, the presence and strength of harmonics, and the duration of different frequency components. These variations contribute to the distinct perception of different vowels and sounds.
Fundamental Frequency: The fundamental frequency, also known as the pitch, corresponds to the lowest frequency component of the sound. When you change vowels or produce different sounds, you alter the fundamental frequency. For example, when you produce a low-pitched vowel like "ah," the fundamental frequency is relatively low. In contrast, a high-pitched vowel like "ee" has a higher fundamental frequency.
Harmonics: Harmonics are integer multiples of the fundamental frequency. They are additional frequency components that give a sound its timbre or tonal color. The relative strengths and presence of harmonics in a sound contribute to its unique character. Vowels and sounds with different timbres have different harmonic structures, which make them distinguishable from each other.
Formants: Formants are specific frequency regions where a sound's energy is concentrated. These formants are responsible for shaping the distinctive characteristics of vowels and sounds. The vocal tract, including the shape and size of the oral cavity, tongue position, and lip shape, acts as a resonator that emphasizes specific frequencies and formants. Changing the shape of the vocal tract alters the resonant frequencies and, therefore, the formants, resulting in different vowel sounds.
Duration and Envelope: The duration and amplitude envelope of a sound affect its perception. Vowels and sounds may have different durations, which can impact how they are perceived. Additionally, the attack, sustain, and decay of the sound's amplitude envelope influence its quality and emotional impact.
When you speak or produce sounds, your vocal cords vibrate to create the fundamental frequency, and the shape of your vocal tract filters and modifies the resulting sound wave. This complex interaction of fundamental frequency, harmonics, formants, duration, and amplitude envelope is what gives rise to the rich variety of vowels and sounds in human speech and natural sounds.
Speech scientists and linguists study these acoustic features to understand how different languages and accents are produced and perceived. It's the subtle variations in these acoustic characteristics that allow us to recognize and distinguish between different vowels and sounds in speech and everyday sounds around us.