In an analog to digital, or digital to analog converter, linearity refers to the ability of the converter to record or reproduce various signals, particularly low level signals, at the correct amplitude. For example, when a bit changes from 0 to 1 in a D/A converter, there must be a corresponding change in the analog signal output. Any non-linearity results in audio signal distortion. For a variety of reasons, it is impossible for a converter to be exactly linear, but high-quality units can come very close. In addition to poor design or quality, non-linearity can result from bit weighting errors, thermal or physical stress, aging, temperature variations, and other factors.