Any subtractive analog synthesizer consists of four essential components: oscillators, a filter, a time-based amplifier and modifiers. The oscillator section is the heart of any synthesizer. These produce the fundamental tones of the instrument. In many early synthesizers, there were only three oscillator waveforms available: square, sawtooth, and triangle waveforms. The most basic waveform is the sine wave. A sine wave is the mathematical sinusoidal function. A sine wave consists of only a fundamental frequency and does not contain any harmonics; therefore, it is audible as a single fundamental tone, comparable to a whistle. A pulse wave is a square wave, but the width of the high and low states are adjustable thereby varying the harmonic content of the sound. A favorite technique in dance music is to layer some synthesized tones from different instruments on top of one another to create broad, exciting sounds.