Hi all,
I am doing a frequency analysis of real signals. I have acceleration data from an impact hammer for six channels. I have calculated psd and Pwelch for each channel. The acceleration data was first filtered with zero phase shift Lowpass IIR Butterworth filter and then Psda and Pwelch are calculated. I have some questions regards my plots:
1.The plotted PSD and Pwelch are very noisy. Is there a way how to obtain more smooth curve for both PSD and Pwelch?
2. Also I have dominating peaks around 0.6Hz. Any idea how these can be removed?
I should mention that acceleration data shown here is cut from an interval that is much longer. Attached you can see the plotted psd and Pwelch and accelration daata used. Also you can see the code I have used.
LP IIR Butterworth:
Nf = 1;
Fpass = 70;
Apass = 1;
Astop = 30;
Fstop = 200;
LP_IIR_B = designfilt('lowpassiir','PassbandFrequency',Fpass,...
'StopbandFrequency',Fstop,'PassbandRipple',Apass,'StopbandAttenuation',...
Astop,'SampleRate',Acc_fs,'DesignMethod','butter');
e = size(WB_Acc_S2_A2_R2);
WB_Acc_S2_A2_R2_Filt = zeros(e);
for i = 1:e(2);
WB_Acc_S2_A2_R2_Filt(:,i) = filtfilt(LP_IIR_B,WB_Acc_S2_A2_R2(:,i));
end
Periodogram:
N = length(WB_Acc_S2_A2_R2_Filt);
fs_A2 = Acc_fs;
NFFT = 2^nextpow2(N);
[Periodogram_S2_A2_R2,freq_A2_R2_Perio] = periodogram(WB_Acc_S2_A2_R2_Filt,[],...
NFFT,fs_A2);
Pwelch:
N = length(WB_Acc_S2_A2_R2_Filt);
fs_A2 = Acc_fs;
NFFT = N;
Noverlap = NFFT/3;
win = NFFT;
wlen = rectwin(win);
[PWelch_S2_A2_R2,freq_A2_R2_PWelch] = pwelch(WB_Acc_S2_A2_R2_Filt,...
wlen,Noverlap,NFFT,fs_A2);
PS This is my first time calculating periodogram and Pwelch.
Many thanks,
Emina
