How to find the Fourier coefficients of an audiofile

I have an audiofile of a bell sound that I want to find the Fourier coefficients of. I have already plotted my data, as well as a spectrogram and a magnitude vs frequency plot but I am not sure how I can use these plots to find the coefficients.

Here is the code:

file = 'Bjall2.m4a';

[x,fs] = audioread(file);

tt = (0:(length(x)-1))/fs;

figure(1); clf;

plot(tt,x);

wz=round(0.05*fs);

hop=round(0,025*fs)

figure(2); clf;

spectrogram(x,wz,hop,1024,fs,'yaxis')

nstart=70000;

xseg=x(nstart:(nstart+wz-1));

X=fft(xseg);

ffn=1:ceil(wz/2);

ff=(ffn-1)/(wz/2);

figure(3); clf;

plot(ff,abs(X(ffn)));

xlabel('Frequency [Hz]')

ylabel('Mag. Spectrum')

figure(4); clf;

data_fft = fft(x);

plot(abs(data_fft(:,1)))

[Mathieu NOE]

hello

what do you mean by Fourier coefficients ? you have already computed the fft values (bins)

do you mean you want to extract the dominant frequencies from the fft / spectrogram ?