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