# Why impulse response

Why do people calculate impulse response? Generally systems are designed after modelling the possible input signals and calculating the appropriate filters for the desired outputs. Where does impulse response calculation become important?

• And how are you going to apply these "appropriate filters" if not by convolving their impulse response with input signal in general? Hence your system is described by... impulse response, isn't it? – jojek Jul 2 '14 at 6:38
• probably the simplest answer to your question is that you bang your system with an impulse and let it ring. you record the ringing response to the impulse and that tells you how the system will respond to any other input. this can be true of any input that is sufficiently broadbanded, but the dirac impulse is simple, completely flat in its spectrum, and has concentrated all of its energy at $t=0$. and it lends itself to the convolution integral better than, say, a unit step. – robert bristow-johnson Jul 2 '14 at 14:20