Here are some movies that illustrate the concepts of
aliasing and folding when a sinusoid is sampled
below the Nyquist rate.
By visualizing the spectrogram of a synthesized chirp and listening to the sound,
we experience the fact that a D-to-C converter cannot create output signals
with frequencies higher than one half of the sampling frequency.
The Continuous-Discrete Sampling Demo (con2dis)
is a program that shows the continuous
and discrete spectra (and signals) during sampling.
- Users can change the input frequency and sampling rate.
- Frequency axis can be labeled in hertz or radians/sec.
- Reconstruction through D/A is also shown.
Here are some movies that illustrate the reconstruction process
These movies give an alternate view of the sampling process
by using the strobing nature of a camcorder (30 frames per
second) to show aliasing of a pattern on a rotating disk.
These movies were generated in MATLAB to show the strobe/sampling
effect on a rotating disk. With MATLAB the rotation rate can be
calibrated exactly, so that forward and backward movement of the
spokes on the disk (due to aliasing) can be tracked.