MATLAB Answers

For Loop Dimensions Not Consistent Horzcat

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Louise Wilson
Louise Wilson on 30 Apr 2019
Commented: Louise Wilson on 30 Apr 2019
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];
csvwrite('output_mean_SPL.csv', meanlevellist);
Error using horzcat
Dimensions of arrays being concatenated are not consistent.

Answers (1)

James Tursa
James Tursa on 30 Apr 2019
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
Louise Wilson on 30 Apr 2019
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.

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