Not only is the voice the principal means of human communication, but it was undoubtedly the first musical instrument. The principal difference between singing and speaking is that in singing the vowel sounds are sustained and given definite pitch. Despite the innate and natural quality of singing, the training of the singing voice for artistic purposes is among the most subtle and difficult branches of music pedagogy. The instrument is within the performer, and the condition of the vocal apparatus, and thus the quality of the voice, is strictly dependent on the physical and mental condition of the singer. Since the vocal impulse cannot actually be described, the teacher's task is to provide the pupil with concepts, usually systematized into a vocal „method,” that will free the vocal apparatus from restrictive tensions and lead ultimately to the complete coordination of all the faculties involved. The foundation of the scientific study of the voice was laid in the middle of the 19th cent. by Manuel Patricio Rodríguez García, a successful voice teacher and writer, who invented the laryngoscope (used to examine the interior of the larynx).
Because of the great changes that have taken place in the art of singing within Western musical culture, modern singers can only approximate the vocal timbre of previous eras. Gregorian chant may have been sung with a nasal timbre resembling Oriental technique. The Neapolitan operatic school developed the virtuoso art of bel canto, in which brilliance of vocal technique was stressed rather than romantic expression or dramatic interpretation. The sound of the castrato (see eunuch), for which many 17th- and 18th-century soprano and alto roles were intended, is approached by several contemporary countertenors using falsetto techniques. The electronic microphone has, in recent times, had an enormous impact on the voice and on styles of singing, through its ability to project very quiet, intimate sounds, and to magnify exciting sounds to a feverish intensity.
Singing voices are classified according to range as soprano and contralto, the high and low female voices, with mezzo-soprano as an intermediate classification; and as tenor and bass, the high and low male voices, with baritone as an intermediate classification. Within these ranges there are specific designations of the quality of a voice, e.g., coloratura soprano. Choral music generally requires a range of about an octave and a half for each voice; a solo singer must have at least two octaves, and some have been known to possess ranges of three, even three and a half, octaves.