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The Nyquist criterion states that, in order to prevent undesired aliasing, one must sample a signal at a rate equal to at least twice its bandwidth. This is often misstated as being "at a rate equal to twice the highest frequency present." Not all aliasing is undesirable. For example, a signal having a 2-KHz bandwidth centered at 455 KHz can be aliased to an offset IF at 1-KHz by sampling it at 4 Khz. Since all 2-KHz bands (0-2 Khz, 2-4 KHz..., 452-454 KHz, 454-456 KHz, 1000-1002 KHz, etc.) are likewise aliased, the signal must have sufficient anti-aliasing filtering applied before sampling to reject the undesired out-of-band content. In addition, one must be careful that the characteristics of the SAMPLE-AND-HOLD circuitry are sufficient to handle the slew rate of the aliased signal, which is directly proportional to frequency.