 A typical example of linear equipment is a high fidelity audio amplifier, which must amplify a signal without changing its waveform.Others are linear filters, linear regulators, and linear amplifiers in general.In most scientific and technological, as distinct from mathematical, applications, something may be described as linear if the characteristic is approximately but not exactly a straight line; and linearity may be valid only within a certain operating region—for example, a high-fidelity amplifier may distort a small signal, but sufficiently little to be acceptable (acceptable but imperfect linearity); and may distort very badly if the input exceeds a certain value, taking it away from the approximately linear part of the transfer function.