Singing is the act of producing musical sounds with the voice, and augments regular speech by the use of both tonality and rhythm. One who sings is called a singer or vocalist. Singers perform music known as songs that can be sung either with or without accompaniment by musical instruments. Singing is often done in a group of other musicians, such as in a choir of singers with different voice ranges, or in an ensemble with instrumentalists, such as a rock group or baroque ensemble. As in many respects human song is a form of sustained speech, nearly anyone able to speak can also sing. Singing can be formal or informal, arranged or improvised. It may be done for pleasure, comfort, ritual, education, or profit. Excellence in singing requires time, dedication, instruction, and regular practice. Professional singers usually build their careers around one specific musical genre, such as classical or rock. They typically take voice training provided by voice teachers or vocal coaches throughout their career.