[Scilab-users] Simulating phase modulation

[Claus Futtrup]

Hi Rafael

Thank you, I shall print and study. :-)

Cheers,
Claus

On Fri, May 25, 2018 at 8:42 PM Rafael Guerra <jrafaelbguerra at hotmail.com>
wrote:

> 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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