[Scilab-users] Simulating phase modulation

[Rafael Guerra]

Hi Claus,

I am not aware of such function. However, you can find simple code here below for both phase modulation and demodulation, which is straightforward to translate in Scilab:
https://www.gaussianwaves.com/2017/06/phase-demodulation-using-hilbert-transform-application-of-analytic-signal/

Note that the phase modulation is coded differently from you snippet below.

Regards,
Rafael

From: users [mailto:users-bounces at lists.scilab.org] On Behalf Of Claus Futtrup
Sent: Friday, May 25, 2018 7:17 PM
To: International users mailing list for Scilab. <users at lists.scilab.org>
Subject: [Scilab-users] Simulating phase modulation

Hi there

In a loudspeaker the driver can move several millimeter in an attempt to reproduce a low-frequency note. If the speaker also at the same time produce a higher tone, this second tone is phase modulated by the first one. This is a distortion of the original signal which I'd like to simulate / illustrate with some simple Scilab code, if possible.

In Matlab this can be simulated with pmmod.
https://matlabandsimulink.wordpress.com/2013/03/12/phase-modulation/

Is there a similar function in Scilab? (name - please ?)

Here's the code I have written so far - this is the part that shows the input signal (the un-distorted signal):


sample_rate=20000;

t = 0:1/sample_rate:0.6;

N=size(t,'*'); //number of samples

y1 = sin(2*%pi*50*t);

y2 = 0.5*sin(2*%pi*500*t);

// y2 = 0.5*sin(2*%pi*500*t+%pi/4);

s=y1+y2+grand(1,N,'nor',0,1);



// Plot time-domain

endplot = round(N/15);

twoplots = scf(); // Set Current Figure (Graphics Window)

subplot(211);

plot(t(1:endplot),y1(1:endplot),t(1:endplot),y2(1:endplot));

subplot(212);

plot(t(1:endplot),y1(1:endplot)+y2(1:endplot));



y=fft(s);

ymax = max(abs(y));

y = y ./ ymax; // Normalize



// s is real so the fft response is conjugate symmetric

// and we retain only the first N/2 points

f=sample_rate*(0:(N/2))/N; //associated frequency vector

n=size(f,'*');

fftplots = scf();

plot(f(2:$),abs(y(2:n))); // drop first datapoint, f = 0 (it prevents log-plot)

a = gca();

a.log_flags = "lnn";

Best regards,
Claus
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