Impulse response means the output of an LTI system when the input is a unit impulse.
eg. $ y[n]=x[n]+2x[n-1]-x[n-2]$
is a system. where, y[n] is the output and x[n] is the input.
Then the unit impulse response of the system is calculated by substituting
$x[n]=\delta[n]$
then, the output $y[n]=\delta[n]+2\delta[n-1]-\delta[n-2]$
ie. impulse response, h[n]={1,2,-1}
Hence values in the impulse response may take any real number.
Impulse response is used to characterize an LTI system. That is if we know the impulse response of a system we can calculate the output for any input x[n] by finding convolution of impulse response (h[n]) with the input(x[n]).
Output of a system with impulse response h[n] and input x[n] is given by the equation (convolution),
$ y[n]= \sum_{k= -\infty}^\infty x[k] h[n-k] $
Here the input x[n] does not have any connection with impulse response h[n].
Note : Unit Impulse is a standard signal with unit amplitude at 0 and 0 at all other instants.
But a unit impulse response is the output of an LTI system when the input is a unit impulse. It is the characteristics of an LTI system and the values may take any real number and is different for different system.
if it is unit impulse response,then it's amplitude should be 1
Oh please. The adjective "unit" qualifies impulse, not impulse response. It is the response to a unit impulse that we are interested in, not the response to some impulse of arbitrary magnitude where the said response has been scaled to have an amplitude of $1$. $\endgroup$ – Dilip Sarwate May 20 '14 at 16:16