the original waveform from its samples. The most common reconstruction technique produces the smallest of the frequencies. So, it is usually important that be the unique minimum. A necessary and sufficient condition for that is called the Nyquist condition. The lower left frame of Fig.2 depicts the typical reconstruction result of the available samples. Until exceeds the Nyquist frequency, the reconstruction matches the actual waveform (upper left frame). After that, it is the low frequency alias of the upper frame.

Folding