Instruments in a Balinese Gamelan orchestra are tuned in pairs: a 'male' and a 'female' instrument. They are tuned slightly apart from each other (just a few Hertz). When both are played together, the slight difference in frequency creates a 'beating' effect—a rhythmic shimmering or pulsing sound known as 'ombak.' This acoustic phenomenon gives the Gamelan its shimmering, vibrant quality. The instruments are considered a single entity and cannot be tuned to a Western piano; each Gamelan set has its own unique tuning.