Adding values to a cell array in a loop for wav files

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Benjamin Colbert
Benjamin Colbert 2022-8-25
评论： Yuqing Li 2022-8-25
I am reading in a wav file in a loop, condcuting and power spectral analysis, and then identifying peaks (by frequency) in a specific band. At the end I need to concatenate the values and spit out a full table that includes all files analyzed. I'm having trouble with " peaks(i) = [pks freq]". I am getting this error "Unable to perform assignment because the indices on the left side are not compatible with the size of the right side." See code:
for i = 941:24:1608; % Start at 4am to avoid chorusing fish or vessels
fprintf('Processing %s\n', char(strcat(Dirin,"\",filelist(i))))
filename = filelist(i);
[filepath,name,ext] = fileparts(filename);
[y,Fs] = audioread(char(strcat(Dirin,"\",filelist(i)))); % read in wav file
samples = length(y);
dt = 1/Fs;
t = (0:dt:(samples-1)*dt);
[sensor_spectrum, freq] = pwelch(y,w,NOVERLAP,NFFT,Fs);
sensor_spectrum_dB = 20*log10(sensor_spectrum) - sensitivity - gain ;
sensor_spec_adj = sensor_spectrum_dB(292:1758); %subsetting db
freq_adj = freq(292:1758); %subsetting frequency
[pks, freq] = findpeaks(sensor_spec_adj, freq_adj, 'MinPeakProminence', 10);
peaks(i) = [pks freq]
name_add = repmat({name},size(peaks(i),1),1)
peaks(i) = [name_add num2cell(peaks)]
end

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回答（2 个）

Star Strider
Star Strider 2022-8-25
Save it to a cell array instead —
peaks{i} = [pks freq]
That should work, since the two vectors being cncatenated will have the same sizes (both assumed to be column vectors).
.
  2 个评论
Star Strider
Star Strider 2022-8-25
Ran in:
As I mentioned ‘(both assumed to be column vectors)’ however apparently, they‘re row vectors, so instead use:
peaks{i} = [pks; freq]
Testing this —
M = randi(9,5,10)
M = 5×10
4 5 6 2 9 4 9 6 4 1 2 9 1 2 2 2 6 4 6 3 4 1 6 2 6 9 3 1 1 3 3 7 3 4 5 9 6 3 7 9 3 8 6 2 2 3 5 6 8 3
freqvctr = linspace(0, size(M,2)-1, size(M,2))*0.1
freqvctr = 1×10
0 0.1000 0.2000 0.3000 0.4000 0.5000 0.6000 0.7000 0.8000 0.9000
for i = 1:size(M,1)
[pks,freq] = findpeaks(M(i,:),freqvctr, 'MinPeakProminence',2.5);
peaks{i} = [pks; freq];
end
peaks
peaks = 1×5 cell array
{2×2 double} {2×3 double} {2×2 double} {2×2 double} {2×2 double}
peaks{1}
ans = 2×2
9.0000 9.0000 0.4000 0.6000
peaks{end}
ans = 2×2
8.0000 8.0000 0.1000 0.8000
The slight changed needed to work with row vectors seems to work.
.

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Yuqing Li
Yuqing Li 2022-8-25
Hello Benjamin,
[pks freq] as the output from function "findpeaks" will be an Nx2 matrix (N being the number of peaks found), but peaks(i) is a scalar. You can iniitialize peaks as a cell array:
peaks = cell(number of iterations,1);
and save [pks freq] in each iteration by:
peaks{i} = [pks freq];
  2 个评论
Yuqing Li
Yuqing Li 2022-8-25
What form of output do you want to get?
Is it a table with filenames in the first column, pks and freq in the second and third column respectively?

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