This demo shows the interesting situation that occurs when we have two sinusoidal signals of slightly different frequencies.

This demo gives the mathematical derivation
of how instrument sounds can be
synthesized using the principles of frequency modulation.
The example sounds include a bell and a clarinet.

This MATLAB demo reconstructs a square, triangle, or
sawtooth waveform, using a given number of Fourier Series coefficients.

Here are four movies showing rotating phasors and
how the real part of the phasor traces out a sinusoid
versus time.
Two of the movies show how rotating phasors of
different frequencies interact to produce complicated
waveforms such as beat signals.

This demo illustrates the connection between a variety of
sounds and their spectrograms. Among the different
sounds are:

This demonstrates the idea of harmonic sinusoids.
Five sinusoids with a common fundamental frequency are
added together, one at a time.