Digital signal processing (DSP) refers to anything that can be done to a
signal using code on a computer or DSP chip. To reduce certain
sinusoidal frequency components in a signal in amplitude, digital filtering
is done. One may want to obtain the integral of a signal. If the signal
comes from a tachometer, the integral gives the position. If the signal is
noisy, then filtering the signal to reduce the amplitudes of the noise
frequencies improves signal quality. For example, noise may occur from
wind or rain at an outdoor music presentation. F iltering out sinusoidal
components of the signal that occur at frequencies that cannot be
produced by the music itself results in recording the music with little wind
and rain noise. Sometimes the signal is corrupted not by noise, but by
other signal frequencies that are of no present interest. If the signal is an
electronic measurement of a brain wave obtained by using probes applied
externally to the head, other electronic signals are picked up by the
probes, but the physician may be interested only in signals occurring at a
particular frequency. By using digital filtering, the signals of interest only
can be presented to the physician.