Implications of Linear Time Invariance (LTI)

LTI systems perform only 4 operations on a signal: copying, scaling, delaying, and adding. LTI systems, can, be reduced to a calculation involving only the sum of phasors, i.e., LTI filters

• modify the amplitude and/or phase of the spectral components of an input signal;
• are guaranteed to produce a sinusoid in response to a sinusoid, without altering the frequency;
• may only attenuate, reject, amplify (boost) or leave unchanged, any existing frequency components of the input signal.