Hi Ejay
I believe you are trying to calculate the cepstral coefficients of the provided signal, specifically the 4th cepstral coefficient.
The link you have provided calculates the real cepstral transform of the signal using fourier transform. This is used for linear frequency spectrum analysis and can be used for checking the periodicity or presence of echoes in a signal.
The 4th cepstral co-efficient can be calculated using the "mfcc" function which estimates the Mel-frequency Cepstral Coefficients of a signal.
coeffs = mfcc(audioData);
coeff_4th = coeffs(K,4,1);
Here "K" refers to the Kth frame whose 4th cepstral coefficient you want to calculate and 1 defines the channel of the audio which you want to analyze.
For more details on how to use the "mfcc" and how to get the 4th cepstral coefficient you can refer to the following link: https://www.mathworks.com/help/audio/ref/mfcc.html
I hope this answers your query.
