I have 3 audios at different speeds and I want to plot the spectrogram as appearing in below figure. Any help for the correction of the code?

clear, clc, close all

[x,Fs]=audioread('1575rpm.wma');

NFFTx = length(x);

x = fft(x,NFFTx);

Fx = ((0:1/NFFTx:1-1/NFFTx)*Fs).';

magnitudex = abs(x); % Magnitude of the FFT

Fx=Fx(1:NFFTx/2);

dBx=[20*log10(magnitudex(1:NFFTx/2))];

Fx=Fx.';

%-----------------------------------------------------------------

[y,Fs]=audioread('1314rpm.wma');

NFFTy = length(y);

y = fft(y,NFFTy);

Fy = ((0:1/NFFTy:1-1/NFFTx)*Fs).';

magnitudey = abs(y);

Fy=Fy(1:NFFTx/2);

dBy=[20*log10(magnitudey(1:NFFTx/2))];

Fy=Fy.';

%-----------------------------------------------------------------

[z,Fs]=audioread('1821rpm.wma');

NFFTz = length(z);

z = fft(z,NFFTz);

Fz = ((0:1/NFFTz:1-1/NFFTx)*Fs).';

magnitudez = abs(z);

Fz=Fz(1:NFFTx/2);

dBz=[20*log10(magnitudez(1:NFFTx/2))];

Fz=Fz.';

%-----------------------------------------------------------------

rpm=[1314;1575;1821];

F=[Fy;Fx;Fz];

N=[dBy;dBx;dBz];

% [F,rpm]=meshgrid(k,rpm);

surf(F,rpm,N)

color bar