The minimum sample frequency that allows reconstruction of the original signal, that is 2W samples per unit distance, is known as the , (or Nyquist rate).The time inbetween samples is called the .

• 如果采样的频率低于这个界限，原信号中频率高于采样频率1/2的频率将会发生“混叠失真”，并在采样得到的信号中以相对低的频率出现。