Creating Frequency Modulated WAV File

Hi guys, I'm fairly new to matlab and I'm trying to create a wav file for an experiment I'm running. I want a 4KHz carrier frequency with a10 Hz modulator frequency which plays for 12 seconds. Based on what I've found online, this is the code i've been using:

clc
close all
clear

%set frequency
f=4000;

%create carrier tone
fs=44100; %sampling rate
d=12; %duration 12 seconds
n=fs*d; %total number of samples
t=(1:n)/fs; %total number of points
y=cos(2*pi*f*t); %function equation

%create modulator tone
fc=10; %rate of modulation
freqdev=40000; %frequency deviation
x=fmmod(y,fc,fs,freqdev);

%generate sound
sound(x,fs);
filename='AStim_4KHz_10Hz.wav';
audiowrite(filename,x,fs)

At the moment the output is just a chirp noise, doesn't sound correct at all. If anyone could point out where I'm going wrong that would be very much appreciated!

Answer 1

[Star Strider]

I’m not certain what you want the result to be.

In situations like this, I plot it (using various methods) to see what the result is, soI know if the code is doing what I want.

That apporoach with your signal produces these results —

% clc
% close all
% clear

%set frequency
f=4000;

%create carrier tone
fs=44100; %sampling rate
d=12; %duration 12 seconds
n=fs*d; %total number of samples
t=(1:n).'/fs; %total number of points
y=cos(2*pi*f*t); %function equation

%create modulator tone
fc=10; %rate of modulation
freqdev=40000; %frequency deviation
x=fmmod(y,fc,fs,freqdev);

figure
plot(t, x)
grid

figure
pspectrum(x, fs)

figure
pspectrum(x, fs, 'spectrogram')
colormap(turbo)

% %generate sound
% sound(x,fs);
% filename='AStim_4KHz_10Hz.wav';
% audiowrite(filename,x,fs)

These require the Signal Processing Toolbox, that also has the modulate function that you can use to cross-check the Communications Toolbox results. (I don’t have the Commmunications Toolbox.)

.