What Is Nyquist Frequency?

Have you ever wondered why your high school math teacher told you to nap after lunch? The answer is simple because they knew the Nyquist frequency would make you sleepy. The Nyquist frequency is a sampling frequency that uses signal processing, defined as "half of the rate" of a discrete signal processing system. The highest frequency can be coded for a particular sampling rate to reconstruct the signal. In other words, if you sample a sound at an audio rate of 44,100 Hz, there will be no frequencies above 22,050 Hz in your sound recording. This means that anything above this frequency will get folded into one or lower frequencies, and all those folded parts are nearly indistinguishable from any other part of the sound wave! Yogis who want to take advantage of their most profound meditative states without losing consciousness have used this phenomenon for centuries. They would sit down and listen to music with an audio rate close to 44,100 Hz until they fell asleep, at which point they'd usually wake up several hours later feeling refreshed and ready to start their day. The Nyquist frequency is one of the essential concepts in signal processing, and it's all about getting a visual signal model. If you've ever tried to listen to a high-pitched whistle while driving down the highway, you know what aliasing is. It's when your ears can't hear a sound at its proper frequency because it's mixed up with other frequencies in the surrounding noise. The same concept applies in sampling: if you sample at less than twice per cycle, you can only build an accurate visual model of the signal if you need more samples per period. The Nyquist theorem states that if you want to represent a signal accurately, you need at least two pieces per cycle of the sampled waveform. If your sampling rate is too low (less than twice per period), there will be gaps in your ability to accurately re-create the original signal from just sampling alone.