In music, texture is how the tempo, melodic, and harmonic materials are combined in a musical composition, determining the overall quality of the sound in a piece. The texture is often described in regard to the density, or thickness, and range, or width, between lowest and highest pitches, in relative terms as well as more specifically distinguished according to the number of voices, or parts, and the relationship between these voices (see Common types below). For example, a thick texture contains many 'layers' of instruments. One of these layers could be a string section or another brass. The thickness also is changed by the amount and the richness of the instruments playing the piece. The thickness varies from light to thick. A piece's texture may be changed by the number and character of parts playing at once, the timbre of the instruments or voices playing these parts and the harmony, tempo, and rhythms used. The types categorized by number and relationship of parts are analyzed and determined through the labeling of primary textural elements: primary melody (PM), secondary melody (SM), parallel supporting melody (PSM), static support (SS), harmonic support (HS), rhythmic support (RS), and harmonic and rhythmic support (HRS).