how to process a random signal with bandpass filter, windowed integrator and maximum amplitude?

Hi all,

I've got a random signal with two vectors; time and pressure. I used a bandpass filter. I droped it here to take a look. I'm not sure if the signal is well filtered.

a=xlsread('Mini_With_Knock.xlsx','A2:A430')
b=xlsread('Mini_With_Knock.xlsx','B2:B430')

plot(a,b)
hold on
d = fdesign.bandpass('Fst1,Fp1,Fp2,Fst2,Ast1,Ap,Ast2',1e3,2e3,20e3,21e3,40,1,40,48e3);
Hd = design(d,'equiripple');
Hd.PersistentMemory = true;
fvtool(Hd);

y = filter(Hd,b);
abs=abs(y)
max=max(abs)

plot(a,y);

Then, I would like to take the maximum amplitude of the signal within a range of time. How could I do that? Should I used a windowed integrator?

Many thanks!