function [pxx,freq] = sprectrum(x,mode,N)
    switch mode 
        case 1
            [pxx,freq] = periodogram(x *sqrt(2*pi),[],N,'centered');
        case 2
            [pxx,freq] = periodogram(x *sqrt(2*pi),hamming(length(x)),N,'centered');
        case 3
            [pxx,freq] = pwelch(x *sqrt(2*pi),[],[],N,'centered');
    end
    pxx = mean(pxx,2);
end