How to plot (1) amplitude vs time and (2) amplitude vs frequency plots from .wav file

Hi, I am having some trouble trying to figure out how to plot an Amplitude vs Frequency plot from a .wav file. I think I managed to figure out how to plot the Amplitude vs Time plot though.

Here is my code:

[y,Fs]=audioread('HornC5.wav'); %Reads .wav file into 2 matrices for amplitude (y) and sampling frequency (Fs)
% sound(y,Fs); % see what it sounds like

y=y(:,1); % Converts to a single channel
dt=1/Fs;
t=0:dt:(length(y)*dt)-dt; %Matrix for time points

% I don't really now how to code the Fourier Transform part :(

figure(1) 
subplot(2,1,1)
plot(t,y); title('Horn C5'); xlabel('Time (s)'); ylabel('Amplitude'); % Amplitude vs Time plot

subplot(2,1,2)
plot

Answer 1

[Star Strider]

The amplitude - Frequency plot would go something like this:

[y,Fs]=audioread('HornC5.wav'); %Reads .wav file into 2 matrices for amplitude (y) and sampling frequency 
L = size(y,1);
Fn = Fs/2;
FTy = fft(y)/L;
Fv = linspace(0, 1, fix(L/2)+1)*Fn;
Iv = 1:numel(Fv);

figure
plot(Fv, abs(FTy(Iv,:))*2)
grid
xlabel('Frequency')
ylabel('Amplitude')

There could be two channels in the .wav file. This will plot both of them in the same plot. Note that ‘Fn’ is the Nyquist frequency, ‘Fv’ is the frequency vector, and ‘Iv’ is the index vector for the plot or other analyses.

I do not have your .wav file so I could not test this with it. It should work.

[Ilada Pathumsiriwan]

Sorry,What is unit of Amplitude? It's Hz or not

Thank you

[Star Strider]

The frequency units (here) are Hz, amplitude is whatever the transducer produced (e.g. mV) or was transformed to (e.g. Pascals if calibrated with respect to Sound pressure level).

It’s complicated!

[Gowri R]

Hi,could you please help to plot this waveform as time in xaxis (milliseconds) and amplitude (microvolts) in y axis.

Answer 2

[Sara Boznik]

figure(1) 
subplot(2,1,1)
plot(t,y); title('Horn C5'); xlabel('Time (s)'); ylabel('Amplitude'); % Amplitude vs Time plot
subplot(2,1,2)
f=1/t
plot(f,y)

I will do it like that.