For Loop Dimensions Not Consistent Horzcat

Hi everyone,

I am new to Matlab and working through code I have found to understand each step. You can see my comments describing in as much detail as I can, what is going on in each step.

This is a for loop which I plan to use to calculate the mean sound pressure level (SPL) of a large batch of sound files.

I understand what is going on in each step and have carried out each in turn, before executing the loop, to make sure everything works.

However, in the last step, where I combing meanlevellist and mean_SPL into an array, I get an error telling my that the dimensions of the two lists are different. I understand what this means in theory but I don't know how to fix it, or see exactly where I have gone wrong, in my code.

ANY advice would be much appreciated!!

I am very keen to develop and advance here.

>> clf; clear all;                                                             %clf-clear current figure; 
                                                                            %clear ALL-clear ALL variables and functions from memory

d = dir('*.wav');                                                           %d=dir lists the names of the files/folders in the current directory
                                                                            %dir('NAME')-lists the files in a folder, * is an asterisk wildcard
                                                                            %MATLAB matches all characters in the name exactly except for the wildcard 
                                                                            %character *, which can match any one or more characters.
                                                                            %so '*.wav' lists all files ending in '.wav' from current directory

                                                                            
                                                                            
                                                                            
                                                                            
meanlevellist = zeros(size(d));                                             %size() returns the size of an array e.g. 70 .wav files
                                                                            %zeros returns a matrix of zeros-this sets aside storage for a matrix
                                                                            %whose elements are to be generated one at a time e.g. 70*0
                                                                            %these are then stored in variable meanlevellist


                                                                            %Now we use a 'for' loop.
                                                                            
                                                                            
for i = 1:length(d)                                                         %length(d) is number of wav files in d so 1-length(d)=1-70, 
                                                                            %so create variable i which has 70 columns     
    filename = d(i).name;                                                   %get the names of all files in d and store in 'filename'
    [dat,fs]=audioread(filename);                                           %[dat,fs]=audioread(filename); returns sampled data in dat and the sample rate Fs in Hz 
    tlo=10; tup=20;                                                         % create time window for plot  -  NB seconds
    nlo=fs*tlo+1;                                                            % first data sample index = sampling frequency * tlo + 1 = 480001
    nup=fs*tup;                                                              % last data sample index  =960000
    data=dat(nlo:nup)';                                                      % data segment for plot/spectrum
    cal = 171.7;                                                             % number taken from calibration sheet
    fact_cal = 10^(cal/20);                                                  % apply calibration
    data=data*fact_cal;                                                      % apply calibration
    npts=length(data);                                                       % number of points in data segment
    tint=npts/fs;                                                            % time interval of data segment
    flo=10;        fhi=100;                                                  % band pass filter bandwidth
    fdata=bandpass(data,[flo,fhi],fs);                                       % apply band pass filter
    pfdata=abs(fdata).^2;                                                    % is Prms^2 of filtered data
    mean_SPL=10*log10(sum(pfdata)/length(pfdata));                           % mean power level, in dB
    meanlevellist(i) = mean_SPL;
    meanlevellist = [meanlevellist, mean_SPL];
end

csvwrite('output_mean_SPL.csv', meanlevellist);
Error using horzcat
Dimensions of arrays being concatenated are not consistent.

Answer 1

[James Tursa]

In these two lines:

    meanlevellist(i) = mean_SPL;
    meanlevellist = [meanlevellist, mean_SPL];

The first line puts mean_SPL into the i'th spot of meanlevellist. Thus it seems to me that the second line is redundant to what you are trying to do. I would suggest getting rid of that second line.

[Louise Wilson]

Hi James!

Thank you for your answer.

Yes, I understand. I am running this now but it's taking a while to run.

Would you agree that perhaps instead of:

    meanlevellist(i) = mean_SPL;
    meanlevellist = [meanlevellist, mean_SPL];
    
    

It would be more intuitive to have:

        meanlevellist(i) = mean_SPL;
    meanlevellist = [filename, mean_SPL];
    
    

??

[Louise Wilson]

It works to remove the last line, as you said, which is very helpful :-)

Removing the last line gives me a list of the mean_SPL values in a 1x5 array.

I would like to have a 2x5 array with the mean_SPL values listed alongside the filenames.

This code runs without errors but it gives me one value in 1x1 cell matrix, clearly wrong.

I can't get this to work? What do you think?

                                                                       
for i = 1:length(d)                                                         %length(d) is number of wav files in d so 1-length(d)=1-70,  
                                                                            %so apply for loop for each data point from 1-70
    filename = d(i).name;                                                   %get filename in d and store in 'filename'
    [dat,fs]=audioread(filename);                                           %[dat,fs]=audioread(filename); returns sampled data in dat and the sample rate Fs in Hz 
    tlo=10; tup=20;                                                         % create time window for plot  -  NB seconds
    nlo=fs*tlo+1;                                                            % first data sample index = sampling frequency * tlo + 1 = 480001
    nup=fs*tup;                                                              % last data sample index  =960000
    data=dat(nlo:nup)';                                                      % data segment for plot/spectrum
    cal = 171.7;                                                             % number taken from calibration sheet
    fact_cal = 10^(cal/20);                                                  % apply calibration
    data=data*fact_cal;                                                      % apply calibration
    npts=length(data);                                                       % number of points in data segment
    tint=npts/fs;                                                            % time interval of data segment
    flo=10;        fhi=100;                                                  % band pass filter bandwidth
    fdata=bandpass(data,[flo,fhi],fs);                                       % apply band pass filter
    pfdata=abs(fdata).^2;                                                    % is Prms^2 of filtered data
    mean_SPL=10*log10(sum(pfdata)/length(pfdata));                           % mean power level, in dB
    meanlevellist(i) = mean_SPL;
    meanlevellist=[meanlevellist, filename];
end

[Louise Wilson]

I have tried this a few different ways but can't get it to work.

Ultimately I want to add my new list of meanSPL values to the existing database.

Could I do this by adding a column to the structure, to make it a 6x1 array?

I'm not sure how to do this but trying to find the solution.