Pitch 

The pitch of musical sounds is a perceptual attribute that allows their classification on a scale of 'high – low.' In general, the perception of pitch is determined by the fundamental frequency of the sound wave. Thus, a sound with a high fundamental frequency typically has a higher pitch than a sound with a lower fundamental frequency. In practice, pitch determines the difference between tones and is a fundamental element of melody and harmony. 

Spectral Centroid 

Spectral centroid is defined as the weighted average frequency of the spectrum, also known as the spectral center of gravity. It has been identified as one of the features with strong perceptual significance and is associated with the perception of acoustic brightness in the literature. Low values usually indicate a "dark" sound, while higher values suggest a "bright" sound. However, it also increases in the presence of noise and tends to fluctuate significantly during transient sound phenomena. If not normalized by dividing by the fundamental frequency (for harmonic sounds) as in this case, it is also strongly correlated with pitch. 

Inharmonicity 

Inharmonicity is a measure of the deviation of the harmonic series from the position of the integer multiples of the fundamental frequency where they should be in the case of a perfectly harmonic signal. There is evidence that singers' voices can be distinguished based on the criterion of inharmonicity. 

Formants 

Formants are local maxima in the frequency spectrum, which, in the study of voice, reflect the resonance frequencies of the human vocal tract. Typically, the positions of the first four maxima, F1, F2, F3, and F4, are calculated. Differences between these allow us to recognize different vowels and distinguish between different speakers or singers. For singers, formants are important because they determine the quality and timbre of their voices. 

Vibrato 

Vibrato is a periodic variation in pitch that creates the sensation of a pulsating sound and is one of the key expressive tools used by singers and performers of string or wind instruments. Particularly for singers, vibrato is considered one of the elements that provide a performer with their unique identity. Vibrato itself is characterized by its rate (the frequency of the variation), its extent (the range of variation around the average value), and its regularity (the extent to which the variation pattern can be approximated by a simple sine wave). Its rate is measured in Hz, its extent in cents (hundredths of a semitone), and its regularity is reflected by a dimensionless quantity derived from the ratio between the amplitudes of the two strongest frequencies contained in the variation pattern. This ratio ranges from 0 for completely irregular vibrato to 1 for vibrato with a simple sine wave pattern with a single variation frequency.