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 digital 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 digital signal quality. For example, noise may occure from wind or rain at an outdoor music presentation. Filtering out sinusoidal components of the digital 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 digital 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. Digital signal processing entails anything that can be done to a signal using coding on a computer or DSP chip. This includes digital filtering of signals as well as digital integration and digital correlation of signals.