Periodogram and Welch periodogram comparison
Looks similar to me 

&gt;  clear all
&gt;     close all
&gt;     load data
&gt;     samplerate=1
&gt;     periodogram (V)
&gt;     title("Periodogram",'FontSize', 14)
&gt;     xlabel('Frequency (Hz)','FontSize', 14)
&gt;     ylabel('Amplitude (dB)','FontSize', 14)
&gt;     
&gt;     figure
&gt;     pwelch(V)
&gt;     title("Welch's method",'FontSize', 14)
&gt;     xlabel('Frequency (Hz)','FontSize', 14)
&gt;     ylabel('Amplitude (dB)','FontSize', 14)