Zouk is a contemporary dance music of the Caribbean that uses both traditional and high-tech musical resources. It is based on interlocking rhythmic and melodic patterns rather than a dense sound where all instruments are played simultaneously. It is connected to a number of Caribbean musical styles such as biguine, merengue, compass direct, cadence, guaguancó, and danzon. Like all of these musical styles, in zouk, rhythm is one of the most significant elements. There are many musical influences on zouk, and the differences between borrowed styles are often smoothed over rather than accentuated. Strong beats are reinforced and the syncopated bass pattern, like that of salsa or funk, is not used. The timbre of the music (its color, the different ways music "sounds") are a vital element in zouk. By using the technical resources available to musicians today, sound can be manipulated to make the familiar sound new. The sound of the conga may be manipulated electronically to give it a variety of sounds. A drum set may receive the same treatment with some parts of the set being left "natural" while others are altered. A basic rule of zouk is to create space in the music by avoiding an overwhelming density of simultaneous parts, allowing the insertion of interesting sounds into the "holes" that are created. Zouk instrumentation usually includes a brass section, two synthesizers, guitar, and bass, and a rhythm section that includes a gourd shaker, conga, drum set, and tumba. The bass line is more than a rhythmic or harmonic instrument, having taken on more of a melodic function. Of the two synthesizers, one acts as a percussion instrument, reproducing what the percussion instruments do, while the other inserts melodic lines at strategic locations. The guitar plays melodic riffs (short repeated melodic phrases) rather than strumming chords, and is also used for solos. The brass section plays in unison, rarely soloing, and is sometimes used to set up counterpoint to the main melody.