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Entry  Tue Nov 29 18:31:40 2011, Den, Update, digital noise, Foton error 
    Reply  Thu Dec 1 18:30:39 2011, Vladimir, Den, Update, digital noise, Foton error 
       Reply  Fri Dec 2 17:43:46 2011, rana, Update, digital noise, Foton error 
          Reply  Wed Dec 7 20:55:44 2011, Vladimir, Den, Update, digital noise, Matlab error gain_cmp.png
Message ID: 6083     Entry time: Wed Dec 7 20:55:44 2011     In reply to: 6062
Author: Vladimir, Den 
Type: Update 
Category: digital noise 
Subject: Matlab error 

Quote:

It would be useful to see some plots so we could figure out exactly what magnitude and phase error correspond to "gross" and "miserable".

To show why Matlab is bad in filtering at small cut-off frequencies we did the same thing in Matab, Octave and R: we've taken the low-pass chebyshev filter of the type 1, order 6, ripple 1 dB, the sampling frequency was 16384 Hz and cut-off frequency varied from 1 to 1000 Hz. Here is the plot for the gain of the zpk model versus to cut-off frequency.

gain_cmp.png

We can see that Matlab's gain shows surprising gains for low cut-off frequencies through for > 100 Hz it is fine. In the next table we compare gain from Foton, Matlab, R and Octave for the same filter. So Foton is also good

freq R_gain matlab_gain octave_gain Foton_gain
1 3.05186270655452e-24 4.8824152e-22 3.05186271e-24 3.05186e-24
10 3.04698335947093e-18 1.8268825e-16 3.04698336e-18 3.04698e-18
100 2.99910841393644e-12 2.9991084e-12 2.99910841e-12 2.99911e-12
1000 2.60247212721439e-06 2.6024721e-06 2.60247213e-06 2.60247e-06
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