Claus Futtrup |
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. 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:$),abs(y(2:n))); // drop first datapoint, f = 0 (it prevents log-plot) a = gca(); a.log_flags = "lnn"; Best regards, Claus _______________________________________________ users mailing list [hidden email] http://lists.scilab.org/mailman/listinfo/users |
Rafael Guerra |
Hi Claus, I am not aware of such function. However, you can find simple code here below for both phase modulation and demodulation, which is straightforward to
translate in Scilab: Note that the phase modulation is coded differently from you snippet below. Regards, Rafael From: users [mailto:[hidden email]]
On Behalf Of Claus Futtrup Hi there In a loudspeaker the driver can move several
millimeter in an attempt to reproduce a low-frequency note. If the speaker also at the same time produce a higher tone, this second tone is phase modulated by the first one. This is a distortion
of the original signal which I'd like to simulate / illustrate with some simple Scilab code, if possible. In Matlab this can be simulated with
pmmod. Is there a similar function in Scilab? (name - please ?) Here's the code I have written so far - this is the part that shows the input signal (the un-distorted signal): sample_rate=20000; t = 0:1/sample_rate:0.6; N=size(t,'*'); //number of samples y1 = sin(2*%pi*50*t); y2 = 0.5*sin(2*%pi*500*t); // y2 = 0.5*sin(2*%pi*500*t+%pi/4); s=y1+y2+grand(1,N,'nor',0,1);
// Plot time-domain endplot = round(N/15); twoplots = scf(); // Set Current Figure (Graphics Window) subplot(211); plot(t(1:endplot),y1(1:endplot),t(1:endplot),y2(1:endplot)); subplot(212); plot(t(1:endplot),y1(1:endplot)+y2(1:endplot));
y=fft(s); ymax = max(abs(y)); y = y ./ ymax; // Normalize
// s is real so the fft response is conjugate symmetric // and we retain only the first N/2 points f=sample_rate*(0:(N/2))/N; //associated frequency vector n=size(f,'*'); fftplots = scf(); plot(f(2:$),abs(y(2:n))); // drop first datapoint, f = 0 (it prevents log-plot) a = gca(); a.log_flags = "lnn"; Best regards, Claus _______________________________________________ users mailing list [hidden email] http://lists.scilab.org/mailman/listinfo/users |
Claus Futtrup |
Hi Rafael Thank you, I shall print and study. :-) Cheers, Claus On Fri, May 25, 2018 at 8:42 PM Rafael Guerra <[hidden email]> wrote:
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Gary Nelson-2 |
Claus, Back in the late 60s, I did my PhD research using analytic signal. Yes,it works, and the implementation details are more complex that we find on the link. A few years ago, I implemented a system for analyzing harbor porpoise vocalizations using scilab. For example, instantaneous phase(t) wants to be differentiable if instantaneous frequency is to be positive. I found that octave bands are the widest that preserves this feature. Yes, you can calculate phase(t) = atan(imaginary/real), but you have to add 2PI when atan wraps around in order to make phase monotonically increase. Also, I am not convinced that a loudspeaker does phase modulation. Certainly, if the speaker is linear, then superposition applies. If phase modulation occurs, it is a non-linear effect. Perhaps that effect is real, but we need to see a model to show how it comes to be. I might be able to help you write analytic signal code. Good wishes Gary Nelson Sent from my Windows 10 phone From: [hidden email] Hi Rafael Thank you, I shall print and study. :-) Cheers, Claus On Fri, May 25, 2018 at 8:42 PM Rafael Guerra <[hidden email]> wrote:
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Claus Futtrup |
Hi Gary Thanks for your input. I went the analytic route for now, and simplified a bit (as you often do with analytic solutions). You're right that from an electro-mechanical point of view, superposition applies, but as the waves transmit in acoustics in air - not, I'm afraid, this is where we see the distortion, simply because the speaker cone moves several millimeter. Best regards, Claus On Sat, May 26, 2018 at 10:55 PM Gary Nelson <[hidden email]> wrote:
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