# Sine wave

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A wave which is "pure" in the sense of the Fourier theorem, which states that all possible waveforms are made up of sums of component sines. As such, applying a filter to a sine wave will have no effect except to increase or decrease the amplitude, depending on the filter parameters; a filter cannot alter a sine waveform by altering the overtones because there are no overtones. As such, the sine wave is not very useful in subtractive synthesis. A sine wave is not very interesting to listen to by itself; however, in additive synthesis, sine waves are combined to make more complex waveforms. On an oscilloscope, a sine wave looks like a series of very smoothly curved alternating hills and valleys. The more commonly used basic waveforms in subtractive synthesis are the triangle wave, pulse wave, and sawtooth wave.

Sine waves are also used as control voltages, for example for FM synthesis, or as an LFO.