How can I ameliorate the trend of a curve ?

Hello

I have to calculate the FFT of the voltage but the trend found is not well.

The curve FRF wanted attached is the best trend.

So How can I ameloirate the trend of this FRF found (figure3 in the program).

Please help me.

The program is:

%% %script traitement signal %objet : traitement signal MPF clc; clear; close all; cd Z:\Matlam\Curves_oscillo_Pc %%

%% load 'data1.txt';

tmp = data1(:,1);

disp = data1(:,2);

acc = data1(:,3);

figure(1)

plot(tmp,acc,'b',tmp,acc,'r.');

xlabel('time (sec)');

ylabel('Acc (ms^{-2})');

%on récupère les données de Oscilloscope en Volt

load 'data1V.txt';

tmpV = data1V(:,1);

Volt = data1V(:,2);

%Voltb = 40e-3*ones(size(tmpV));

figure(2)

plot(tmpV,Volt,'b',tmpV,Volt,'r.');

xlabel('time (sec)');

ylabel('Voltage(V)'); %%

L=length(tmp)

Lv=length(tmpV)

Fs = 5000; % Sampling frequency

NFFT = 2^nextpow2(L) % Next power of 2 from length of y

NFFTV = 2^nextpow2(Lv) % Next power of 2 from length of y

figure(3)

VOLT = fft(Volt,NFFT)/L; % Calcul de la FFT

amplitude = 2*abs(VOLT(1:NFFT));

f = Fs/2*linspace(0,1,NFFT/2);

semilogy(f(1:NFFT/12),2*abs(VOLT(1:NFFT/12)))

xlabel('frequency')

ylabel('FRF Volatage')