[Scilab-users] Frequency response

[Claus Futtrup]

Hi Samuel and Scilabers

My problem with freq and repfreq is that they require a "sys" input, 
which implies I need to describe a response function of some sort. For 
example (from the Scilab web-help):

https://help.scilab.org/docs/6.0.1/en_US/freq.html (example code)

s=poly <https://help.scilab.org/docs/6.0.1/en_US/poly.html>(0,'s');
sys=(s+1)/(s^3-5*s+4)
rep=freq(sys("num"),sys("den"),[0,0.9,1.1,2,3,10,20])

https://help.scilab.org/docs/6.0.1/en_US/repfreq.html (syntax)

[ [frq,] repf]=repfreq(sys,fmin,fmax[,step])
[ [frq,] repf]=repfreq(sys[,frq])
[ frq,repf,splitf]=repfreq(sys,fmin,fmax[,step])
[ frq,repf,splitf]=repfreq(sys[,frq])


... So, the thing with the matlab freqz (as the example repeated below 
shows) is just a basic FFT with sampling, etc:

h = rand(1,64); // impulse response (Matlab source code)
fs = 1000;
Nfft = 128;
[H,F] = freqz(h,1,Nfft,fs);
semilogx(F,mag2db(abs(H))); grid on;
xlabel('Frequency (Hz)'); ylabel('Magnitude (dB)');

It may very well be that I just don't understand the help page of 
repfreq. For example it says about sys: "A siso or simo linear dynamical 
system, in state space, transfer function or zpk representations, in 
continuous or discrete time." - al right then, it seems pretty capable, 
but so, what's "zpk" for example? ... my apologies for finding the 
Scilab help to be cryptic and the examples insufficient for me to solve 
my problem, hence I ask if someone can take above matlab code and make 
it work in Scilab.

Best regards,
Claus

On 15.09.2018 00:32, Samuel Gougeon wrote:
> Le 14/09/2018 à 20:57, Claus Futtrup a écrit :
>>
>> Dear Scilabers
>>
>> I have calculated an impulse response and wish to do an FFT to 
>> achieve the frequency response. I know what to expect. In the matlab 
>> forum someone asked the same question and was recommended to use 
>> freqz ... I wonder what would be the equivalent function in Scilab?
>>
>> https://www.mathworks.com/matlabcentral/answers/350350-how-to-plot-loudspeaker-frequency-response-from-its-impulse-response 
>>
>>
>> For example, to replicate the code snippet (second answer in above 
>> link), how to do this in Scilab?
>>
>> h = rand(1,64); // impulse response (Matlab source code)
>> fs = 1000;
>> Nfft = 128;
>> [H,F] = freqz(h,1,Nfft,fs);
>
> Did you have a look around freq() or repfreq()?
>
> We have somewhat the equivalence invfreqz(H,F,m,n,W) <=> 
> frfit(F*2*%pi, H, n, W) // Scilab
>
> So you may look for the reciprocal of Scilab's frfit()
>
> HTH
> Samuel
>
>
>
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