A form of amplitude distortion that results in the flattening of an output waveform. In analogue systems clipping can be caused by improper setting of the bias voltage, especially in transistor circuits. When clipping occurs at the output of an amplifier and is due to the input-signal amplitude being too large, the amplifier is said to be overdriven. In some circumstances, such as a guitar distort, the effect is produced quite deliberately. In digital systems clipping occurs when adjusting the gain or filtering of a signal produces a result that falls outside the allowed range of discrete values. For example, Compact Disc Digital Audio is based on a 16-bit PCM digital signal that has a resolution of 216, or 65 536 values. If this represents signed integers in the range [–32 768, 32 767], then any operation on a signal that produces values outside this range will result in truncation of the result to the allowed extreme value. See audio clipping.