Bode plot

A Bode magnitude plot is a graph of log(magnitude) against log(frequency) often used in signal processing. It makes multiplication of magnitudes a simple matter of adding distances on the graph, since log(a×b) = log(a)+log(b). The Bode plot describes the output response of a frequency-dependent system for a normalised input.

A Bode phase plot is a graph of linear (phase) against linear frequency used (most times) in combination to evaluate how much a frequency will be phase-shifted. For example a signal described by: A×sin(ωt) may be attenuated but also phase-shifted. If the system attenuates it by a factor x and phase shifts it by -Φ the signal out of the system will be A/x×sin(ωt-Φ). The phase shift Φ is often a funktion of the frequency.

The Magnitude- & Phase Bode Plot can seldom be changed one independent of the other, if you change the magnitude of the system you will most likly change the phase characteristics aswell and vice verce.

A typical application of a Bode plot is to show the frequency response of a filter. It is especially useful in this case because the complex curves that appear in a linear magnitude-frequency plot can be approximated by straight lines in a Bode plot.

Also see Transfer funktion