Singing is the act of producing musical sounds with the voice, and augments regular speech by the use of tonality, rhythm, the use of sustained tones and a variety of vocal techniques. A person who sings is called a singer or vocalist. Singers perform music (arias, recitatives, songs, etc.) that can be sung without accompaniment or with 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. Singers may also perform as soloist with accompaniment from a piano (as in art song and in some jazz styles) or with a symphony orchestra or big band. There are a range of different singing styles, including art music styles such as opera and Chinese opera, religious music styles such as Gospel, traditional music styles, world music, jazz, blues and popular music styles such as pop and rock.