Waveform
Overview
The term "waveform" is used to describe the shape or "form" of a wave signal. The term "wave" is commonly used to describe a cyclical electromagnetic signal or acoustic signal because of the similarity to "waves" in a body of water.
Basics
At the most basic level, a “sine” waveform represents a single frequency or “pure tone.” Most audio waveforms consist of multiple frequencies with varying phase relationships; which results in a very different shape than a sine wave. Using the technique of Fourier analysis; even complex waveforms can be broken-down into the constituent sine wave components.
For more information on Fourier analysis; click here.
Because the constituent sine waves of a complex waveform add or subtract from each other due their phase relationship; the shape of the waveform can vary over time; even if the amplitude and frequency of the constituent sine waves do not. In a similar manner, even if the waveform consists purely of harmonic frequencies; the phase relationship of each harmonic frequency component will affect the shape of the resulting complex waveform. This is part of the reason why using square waves with a near zero rise-time or extremely short impulses in testing audio circuitry is usually not relevant to circuit performance with audio signals. The only way a "square edge" waveform can exist is if every harmonic frequency remains perfectly "in-phase" with each other, and harmonics extending into the hypersonic frequencies are included. Although it is possible to generate square or square-edge pulse waveforms using a synthesizer or test equipment; real-world music (and most other audio) never contains square edge waveforms because limiting the signal's frequency response will result in a finite rise-time (or in other words a less than infinitely steep slope to the rising edge of the waveform). Virtually all audio is frequency-band limited for a number of reasons; including real limitations in audio performance caused when higher-than-audio frequencies are allowed to pass though audio amplifiers or digital audio converters.
for more information on hypersonic frequencies in digital audio, click here