Can't understand why Pwelch claims window is larger than input signal

segment_length = 1229;

hannw = hann(segment_length);

overlap_length = round(segment_length / 2);

disp(size(SuperTrialH2Hit))

returns 30 207701

[pxx4HH, hz4HH] = pwelch(SuperTrialH2Hit, hannw, overlap_length, nextpower2(numel(SuperTrialH2Hit)), SR);

returns

Error using signal.internal.spectral.welchparse>segment_info (line 345)

The length of the segments cannot be greater than the length of the input signal.

Error in signal.internal.spectral.welchparse (line 34)

[L,noverlap,win] = segment_info(M,winp,noverlap1);

Error in welch (line 56)

signal.internal.spectral.welchparse(x,esttype,args{:});

Error in pwelch (line 174)

[welchOut{1:nargout}] = welch(x,funcName,inputArgs{:});

Answer 1

[William Rose]

@Jude,

[Edit: correct spelling in my comments.)

You need to use the transpose of the data array. pwelch() finds the spectrum of each column, when the input data is an array. And in your array, the data whose spectra you wish to compute are in rows. See the following, which runs without error.

SuperTrialH2Hit=rand(30,207701);
SR=1; % sampling rate
segment_length = 1229; 
hannw = hann(segment_length);
overlap_length = round(segment_length / 2);
disp(size(SuperTrialH2Hit)) 

          30      207701

[pxx4HH, hz4HH] = pwelch(SuperTrialH2Hit', hannw, overlap_length, ...
    nextpow2(numel(SuperTrialH2Hit)), SR);

Good luck.

[William Rose]

@Jude, I'm surprised your code ran, because it uses nextpower2(), which is not a built-in function. I changed it to nextpow2() for my example above.

Answer 2

[Jude]

Hiya!

Simple, thank you for taking the time. I actually made my own nextpower2 function as I didn't realise there was one built in!!!!

Jude