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.