Aliasing (Du. vouwvervorming) is the phenomenon of the ambiguity of a sampled signal.
With a sampling frequency of 10 kHz, a sine wave with a frequency of 3 kHz receives the same representation as a sine wave with a frequency of 7 kHz, 13 kHz, or 17 kHz, and so on. If the sampled signal is meant to represent a continuous spectral range starting at 0 Hz (which is the most common case for speech recordings), all these tones are likely to be interpreted as 3 kHz tones after sampling.
To remedy this unwanted situation, the signal is usually low-pass filtered with a cut-off frequency just below 5 kHz, prior to sampling.
© ppgb, March 31, 2004