How to create siren sound using makesound

Dear all,

I am trying to generate sound which follows an amplitude signal. Means, when amplitude of my signal is increasing, my frequency is too, etc ..

To start as simple, I made different consecutive sounds with different frequencies to first understand the principle, playing well. Then increased the complexity by generating a vector which represents the frequency variation of my sound. I did it as sinusoidal, should sound like a siren.

Then using this variable frequency vector, I generate the sound using the sound function. At the end, I can hear the frequency varying but also constantly increasing and I don't understand why. Could you please tell me what is wrong here ? I am pretty sure I'm facing very basic misunderstanding ...

Thank you in advance !

% create the frequency oscillation "siren" frequency, between 200 and 400Hz, oscillating at 1Hz.
time = 0:0.001:5;
f = 100*sin(2*pi*1*time) + 300;

fs=44100; % sample rate

% setup the nb of points according to time length of the signal and sample
% rate

d=time(end); %duration
n=fs*d; % number of points
t=(1:n)/fs;

% Interp the previous frequency vector to fit the new time vector
f = interp1(time,f,t);

% Generate the signal
y=sin(2*pi*f.*t);

sound(y,fs);

Answer 1

[Mathieu NOE]

hello

You have to remember that the output is the sinus of an angle, which is the integral of frequency over time;

so when frequency also varies with time , it's incorrect to simply make the product of 2*pi*f*t, you have to do the integral with cumtrapz as shown below :

I also simplified a bit your code (only one time vector needed)

fs=44100; % sample rate
dt = 1/fs;
t = 0:dt:5;
f = 100*sin(2*pi*1*t) + 300;

% Generate the signal
angl = cumtrapz(t,f); % angle is integral of frequency
y=sin(2*pi*angl);
sound(y,fs);

[Pierre-Alexandre Blot]

Thank you so much ! It's now working and I could even go further in what I wanted to do (frequency following a given input signal). Thank you again for explanations ;)

[Mathieu NOE]

my pleasure !

would you accept my answer ?