Pad ratio

原文

Pad ratio

Why? To improve frequency resolution

Pad ratio is another parameter that can be modified to select an analysis most suitable for identifying key features in your data. Padding is literally that – it involves adding zeros to your signal to make it longer, which improves frequency resolution.

Make complex signal with long and short bursts of power at 8 and 45 Hz

%-----------------------------------------------------------------------------------
% Make complex signal with long and short bursts of power at 8 and 45 Hz
%-----------------------------------------------------------------------------------
D = 2; %signal duration 2s
S = 1000; % sampling rate, i.e. N points pt sec used to represent sine wave
F = [8 8 45 45]; % 4 frequencies in Hz
w = 2*pi*F; % convert frequencies to radians
P = [0 0 0 0]; % 4 corresponding phases
T = 1/S; % sampling period, i.e. for this e.g. points at 1 ms intervals
t = [T:T:D]; % time vector %corrected from previous version
t=t(1:length(t)-1); % takes off extra point arising from starting at zero
nfreqs=length(F); % N frequencies in the complex
A=ones(nfreqs,length(t)); %amplitudes initialised at one
A(1,550:570)=3; %burst of increased amplitude at each time pt
A(2,700:900)=3;
A(3,950:970)=3;
A(4,1100:1300)=3;
% Add all sine waves together to give composite
for thispt=1:2000
for thisfreq=1:nfreqs
mysig(thisfreq,thispt) =A(thisfreq,thispt)*sin(w(thisfreq)*t(thispt));
end
end
mysig2=sum(mysig,1);
t=t-.5; %subtract 500 ms to indicate baseline is negative
figure; plot(t,mysig2);
xlabel('Time (seconds)');
ylabel('Amplitude');
scrsz = get(0,'ScreenSize');

Testing different pad ratio and save plots

n=1
for pr=[.5, 1,2,4,8,16] %pad ratio
    n=n+1
cyc=[1 ]; % cycles (can experiment with different values)
fig=figure('Position',[1 scrsz(4)/4 scrsz(3)/2 scrsz(4)/3])
[ersp,itc,powbase,times,freqs]=...
newtimef( mysig2,2000,[-500 1500],1000, cyc, 'erspmax', 20, 'plotitc', 'off', 'padratio',pr);
title(strcat('Pad ratio= ',num2str(pr),': N freqs=',num2str(length(freqs))));
print(fig,['10-',num2str(n)],'-dpng')
end