# Difficulty : Impulse response and Convolution

1. Nov 21, 2011

### salil87

Hi
We can find the response to a system with any input f(t) if we know the impulse response h(t) of that system. I can also understand the ∫f(τ).h(t-τ)dτ in the τ domain i.e. invert the h(τ) around the vertical axis and shift on the τ axis using t as the shift. But I am not understanding how to visualize it as a sum of the shifted h(t) signals on the t axis i.e. you shift h(t) by τ and you get h(t-τ) then you multiply it by f(τ). Atlast you sum all such shifted functions.
This Confusion arose when h(t) = f(t) = u(t) where the answer is t.u(t). This is because while visualizing in the τ domain, i.e. inverting h(τ) around the vertical axis I can understand. But when I try to visualize that h(t) is shifted by value τ and multiplied by the value f(τ) and then all such shifted functions summed I feel that the ramp should start from 1 not from zero. I dont know how I can't come out of this confusion. Please if you can do help me out.
Thanks
Salil