I am doing an IFFT of frequency response data achieved with Simulation tools. 

When I plot my impulse response it looks wrong as the response does not tend to zero as it should. Instead there seems to be a rise in pressure towards the end of the signal.

My script looks like this:

```
close all;
clear all;
A = load('PvaluesAtReceiver.txt');
f = A(:,1);
Preal = A(:,2);
Pimag = A(:,3);
Prealpad = cat(1,Preal,zeros(48000-180,1));
Pimagpad = cat(1,Pimag,zeros(48000-180,1));
fpad = cat(1,f,zeros(48000-180,1));
enter preformatted text here
j = sqrt(-1);

Prealf = Prealpad(88:177);
Pimagf = Pimagpad(88:177);
ff = fpad(88:177);
Prealfpad = cat(1,Prealf,zeros(48000-90,1));
Pimagfpad = cat(1,Pimagf,zeros(48000-90,1));
ffpad = cat(1,ff,zeros(48000-90,1));
X_ff = Prealfpad + j*Pimagfpad;
X_ff = [zeros(ff(1),1); X_ff];
IRf = ifftshift(X_ff);
x_tf = ifft(IRf);
figure,plot(real(x_tf)), title('Impulse response filtered');

```

This produced the following plot:

[![enter image description here](https://i.stack.imgur.com/KxQLD.png)](https://i.stack.imgur.com/KxQLD.png)

Does anyone know why this doesn't tend to zero?? 

---

[![enter image description here](https://i.stack.imgur.com/smVHh.png)](https://i.stack.imgur.com/smVHh.png)

This is the frequency domain i want to transform.