# Frequency modulation to a digital signal

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Haman Siu am 25 Feb. 2018
Kommentiert: Haman Siu am 25 Feb. 2018
So I have a digital sound signal that i am trying to have its frequency being modulated by a sinusoidal waveform. I tried to used the following code to create the effect but then realize that all it does is moving samples around creating noise rather than creating the effect that i wish to create does anyone have any idea how to create a piece of code to apply FM to a digital audio file?
duration = size(x);
index = 1 : length(x);
time_delay = 0.04;
delay = ceil(time_delay*Fs);
Fc = 20;
a= 1;
b= 1;
modulation_argument = 2*pi*Fc/Fs
;
for i= delay+1:1:duration
modulation(i)=sin(modulation_argument*i);
delay2 = round(delay + modulation(i));
d=(i-delay2);
z(i) = a*x(d);
end;
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### Antworten (1)

John BG am 25 Feb. 2018
Hi Haman
1.
do you want to use the function fmmod?
y = fmmod(x,Fc,Fs,freqdev)
It does the job and save you time.
Fs is the frequency of the modulating tone.
.
2.
You can shift the phase (< 1 cycle) a constant value adding the optional phase shift.
y = fmmod(x,Fc,Fs,freqdev,ini_phase)
.
3.
If interested to know more how does fmmod work then check
.
4.
Use fmdemod to FM demodulate, either to recover signal, or just to check fmmod works ok.
.
5.
Also, perhaps you would like to switch to Simulink.
Simulink has a really powerful array of blocks for signals modulation.
.
6.
A few toolboxes that you may find interesting:
Communications Toolbox:
DSP Systems Toolbox:
.
Haman
John BG
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Haman Siu am 25 Feb. 2018
I do not have access to the fmmod function as its not included in my licence and I am working with the code for a project, so simulink is not an option for me

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