Aliasing matters when one attempts to reconstruct the original waveform from its samples. The most common reconstruction technique produces the smallest of the f N ( f ) frequencies. So it is usually important that f 0 ( f ) be the unique minimum. A necessary and sufficient condition for that is f s / 2 > | f | , called the Nyquist condition. The lower left frame of Fig.2 depicts the typical reconstruction result of the available samples. Until f 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.