Editing Nonlinear distortion (section)

==Model==
For many devices, a linear model is accurate only for small signal levels. For example, at 2 [[volt]]s input, a typical audio [[amplifier]] might put out 20 V, meaning the linear gain is 10  V/V. For 3 V input, it might then output 30 V. However, the model implies that at 50 V input it would produce 500 V, which is not possible with most amplifiers.

Mathematically, the input-output relationship of many devices should be described by a [[polynomial]] or [[Taylor series]], as shown below.

<math>v = \sum_{k=1}^\infty a_ku^k</math>

For larger values of ''u'', the higher order coefficients such as <math>a_2</math> and <math>a_3</math> come into play.