Arguably, all music can be said to be useful for Meditation. The styles, cadences, arpeggiations, and rhythms of meditational music for contemplative practices is characteristically different than most other forms of music. Generally speaking, the music is relaxing, lacking definitive rhythms. Meditation and music have been relational partners for centuries. Mellow, repetitive, and redundant sequences of smoothly contoured melodic lines help to relax the mind as arrhythmic tempos do not distract the listener into a beat but rather a flow. Harmonies are often absent unless one accepts the musical nuance of imitation as structured harmony. Meditation music can also include recordings of sounds in the "natural" world: rainfall, waterfalls, birds, insects, whales, and others, separately and in synthetic combination.