Error on Undefined function 'log' for input arguments of type 'cell'.

close all;
%{Step 0: Reading the File & initializing the Time and Freq.
    [x,fs]=audioread('baby-crying-sleepy.wav');
    x=x(:,1);
    ts=1/fs;
    N=length(x);
    Tmax=(N-1)*ts;
    fsu=fs/(N-1);
    t=(0:ts:Tmax);
    f=(-fs/2:fsu:fs/2);
    figure, subplot(411),plot(t,x),xlabel('Time'),title('Original Speech');
    subplot(412),plot(f,fftshift(abs(fft(x)))),xlabel('Freq (Hz)'),title('Frequency Spectrum');

%%Step 1: Pre-Emphasis

    a=1;
    b=[1 -0.95];
    y=filter(b,a,x);
    subplot(413),plot(t,y),xlabel('Time'),title('Signal After High Pass Filter - Time Domain');
    subplot(414),plot(f,fftshift(abs(fft(y)))),xlabel('Freq (Hz)'),title('Signal After High Pass Filter - Frequency Spectrum');

%%Step 2: Frame Blocking

    frameSize=256;
    frameOverlap=128;
    frames=enframe(y,frameSize,frameOverlap);
    NumFrames=size(frames,1);

%%Step 3: Hamming Windowing

    hamm=hamming(256)';
    for i=1:NumFrames
    windowed(i,:)=frames(i,:).*hamm;
    end

%%Step 4: FFT 
%Taking only the positive values in the FFT that is the first half of the frame after being computed. 

    for i=1:NumFrames
    fft(i,:)=abs(windowed(i,:))*(frameSize/2);     
    end

%%Step 5: Mel Filterbanks
%Lower Frequency = 300Hz
%Upper Frequency = fs/2
%With a total of 22 points we can create 20 filters.
    Nofilters=20;
    lowhigh=[300 fs/2];
    %Here logarithm is of base 'e'
    lh_mel=1125*(log(1+lowhigh/700));
    mel=linspace(lh_mel(1),lh_mel(2),Nofilters+2);
    melinhz=700*(exp(mel/1125)-1);
    %Converting to frequency resolution
    fres=floor(((frameSize)+1)*melinhz/fs); 
    %Creating the filters
    for m =2:length(mel)-1
        for k=1:frameSize/2
     if k<fres(m-1)
        H(m-1,k) = 0;
    elseif (k>=fres(m-1)&&k<=fres(m))
        H(m-1,k)= (k-fres(m-1))/(fres(m)-fres(m-1));
    elseif (k>=fres(m)&&k<=fres(m+1))
       H(m-1,k)= (fres(m+1)-k)/(fres(m+1)-fres(m));
    elseif k>fres(m+1)
        H(m-1,k) = 0;    
     end 
        end
    end
    %H contains the 20 filterbanks, we now apply it to the
    %processed signal.
   bankans=cell(NumFrames,Nofilters);
for i=20:1
for j=1:256
        bankans{i,j}=sum(fft(:,i).* H(j,:));
    end
    end


%%Step 6: Neutral Log and DCT
    %pkg load signal
    %Here logarithm is of base '10'
    logged=log(bankans);
    for i=1:NumFrames

        mfcc(i,:)=dct2(logged(i,:));
    end

%plotting the MFCC

    figure 
    hold on
    for i=1:NumFrames
        plot(lnd(i,:));
    end
    hold off

Can some help me fixing the error?

Answer 1

[Walter Roberson]

your code uses .* between a row vector and a column vector . That is an error in r2016a and earlier but valid in r2016b and later where it will produce a 2d array. you sum() the array which will give a row vector . You store the row vector as an entry in the 2d cell array bankans .

You then try to log the entire cell array bankans which is failing because log is not on operation for cells . You need to arrayfun the log operation which would get you a 2d cell array logged. You also need to consider using log10 as log is natural log.

once you have the log in logged you proceed to dct2(logged(i,:)) where i is a frame number . This is asking for dct2 of an entire row of a cell array each entry of which is a row vector . That will fail. What could potentially work is dct2(vertcat(logged{i,:})) which would arrange the row of row entries into a 2d array that it could potentially make sense to take dct2 of. The result would be a 2d array .

You then take the 2d array and try to store it as a row of mfcc. That will fail . But we know that a 2d result is intended because you would have used dct instead of dct2 if you expected a row result . So you will need to change mfcc to a cell array or to 3d.

After that you ignore mfcc and plot a variable that does not exist. Hard to deduce a meaning there .

It looks to me as if someone translated some python code to MATLAB and made mistakes .