Why am I unable to add these elements to an array?

I'm currently working on a project where I am creating music from the intensities of an image, and I'm able to produce the overall sounds through a for loop, but I am running into a new error -- I am trying to take all of these frequencies and write them using audiowrite, but I am getting an error that says "Unable to perform assignment because the size of the left side is 1-by-4096 and the size of the right side is 1-by-8192." I am using code from a previous project where I did something similar in creating an array of sounds, so I don't understand why I am getting this error now.

%% SNIPPET OF CODE FROM MAIN FUNCTION
for currentImage = 1:length(allImgs)
    filename = allImgs(currentImage) + ".wav";
    img = imread(allImgs(currentImage));
    [imGray, histMtx, binEdge, notes, songLength] = mus306GenerateNotes(img);
    fs = 44100;
    time = 1;
    values = 0:1/fs:time;
    rate = 32768;
    for i = 1:songLength
        currentNote = notes(i);
        singleNote = mus306NoteFinder(currentNote);
        [currentOct, ~] = mus306NoteFinder2(currentNote);
        octaves(i) = currentOct;
        finalNotes(i) = singleNote;
    end
    secondImg = img;
    secondImg(:) = ones(size(secondImg)) * 255;
    [r,c,~] = size(img);
    for i = 1:songLength
        noteLength = durations(randi(durationOption));
        octToHear = octaves(i);
        note = @(t,freq,oct) sin(linspace(0,2*pi*t*freq*2^oct,round(t*rate)));
        % noteSound = sin(linspace(0,2*pi*noteLength*finalNotes(i),...
        %     round(noteLength*rate)));
        noteSound = note(noteLength, finalNotes(i), octToHear);
        % ERROR IN LINE BELOW: Unable to perform assignment because the
        % size of the left side is 1-by-4096 and the size of the right side
        % is 1-by-8192. (i can't figure out how to change the color of this
        % to red, apologies)
        allNotes(i,:) = noteSound;
        sound(noteSound, fs)
        pause(0.1)
        for row = 1:r
            for col = 1:c
                if (imGray(row, col) == i)
                    secondImg(row, col,:) = img(row, col, :);
                end
            end
        end
        audiowrite(filename, allNotes, fs);
    end
    
    %% CUSTOM FUNCTION MUS306GENERATENOTES.M
    function [imGray, histMtx, binEdge, notes, songLength] = mus306GenerateNotes(imgToSee)
    audibleMin = 200;
    audibleMax = 1000;
    imGray = rgb2gray(imgToSee);
    [histCount, binEdge] = histcounts(imGray(:), 0:255);
    histMtx = [binEdge(1:end-1)', histCount'];
    figure(1)
    notes = histMtx(:, 2);
    songLength = length(notes);
    for i = 1:songLength
        audibleNote = notes(i);
        if ((audibleNote / audibleMin) < 1)
            audibleNote = audibleNote * 10;
            if ((audibleNote / audibleMax) > 1)
                audibleNote = audibleNote / 10;
            end
        elseif (((audibleNote / audibleMax) > 1))
            audibleNote = audibleNote / 10;
            if ((audibleNote / audibleMin) < 1)
                audibleNote = audibleNote * 10;
            end
        end
        notes(i) = audibleNote;
    end
    end

[Torsten]

And the riddle for us is to find out in which line of your code the error happens ?

[Yamini]

Apologies, I thought I added in a comment to show where my code is failing. The comment has now been added with the error my system is returning.

Answer 1

[Walter Roberson]

        noteLength = durations(randi(durationOption));

A duration is randomly selected

        note = @(t,freq,oct) sin(linspace(0,2*pi*t*freq*2^oct,round(t*rate)));

A function is constructed in which the size of the output vector depends on the first parameter.

       noteSound = note(noteLength, finalNotes(i), octToHear);

The randomly-chosen duration is passed to the function in the slot the determins the length of the output vector. Therefore, noteSound is a random size.

      allNotes(i,:) = noteSound;

The randomly-sized vector is written to a complete row of allNotes.

allNotes was not defined before that statement first executes, so that statement is going to succeed the first iteration. However, the next time that the statement executes with a different random length, the number of columns in noteSound (determined by the duration randomly chosen) is not going to match the number of columns in the existing allNotes array.

        audiowrite(filename, allNotes, fs);

audiowrite() treats columns as channels. If everything went well then allNotes is a 2D array with rows according to number of notes, and columns containing the sin information for the note. That is clearly the wrong way around: the time series data for notes must be down columns rather than across columns in order for the time series data to be stored properly. If you were to audiowrite passing in allNotes.' then the individual notes would become different channels. You are writing a .wav file and audiowrite supports up to 1024 channels for .wav files.

I doubt this is what you want to do, but since you are constructing 2D arrays of the sine information, then maybe it is...

[Yamini]

Oh, I see now. Would it still be possible for me to add the elements if I preallocate the size of allNotes before my loop, or is it still not possible? I really don't understand why I was able to implement this code in a project before and it worked perfectly, but when I try it with this new code it is failing. I can upload the previous project's code for reference if necessary. Thank you for all your help!

[Image Analyst]

Please attach a file for which the code fails. Zip it up if you have to.

[Yamini]

I have now attached my file -- thank you!

[Walter Roberson]

Before

    for i = 1:songLength

insert

    allNotes = cell(songLength,1);

Change

    note = @(t,freq,oct) sin(linspace(0,2*pi*t*freq*2^oct,round(t*rate)));

to

    note = @(t,freq,oct) sin(linspace(0,2*pi*t*freq*2^oct,round(t*rate))) .';

now change

    allNotes(i,:) = noteSound;

to

    allNotes{i} = noteSound;

Change

        audiowrite(filename, allNotes, fs);

to

        audiowrite(filename, cell2mat(allNotes), fs);

[Yamini]

That worked perfectly!! Thank you so much for all your help!