juha_p wrote: ↑
Sun Oct 10, 2021 6:10 am
SKyzZz wrote: ↑
Sun Oct 10, 2021 4:43 am
The fact is that there is no destructive solution. HP filter works fine. But the problem is the LP filter. I also gave examples of what the problem is. There are a lot of comments on these two topics, but there is not a single solution to this problem...
IIRC, response you get for CURRENT plot means your coefficient order is reversed or mixed.
Did you try plot using Earlevel's grapher
Assume: Fc = 0.25 (normalized frequency, equivalant to ~11 KHz at 44100 sample rate)
For 1st order LPF, use the mentioned:
b1 = exp(-2.0 * M_PI * Fc);
a0 = 1.0 – b1;
b1 = 0.20787957635076193
a0 = 0.7921204236492381
Copy paste these two params to the “filter frequency response grapher”:
http://www.earlevel.com/main/2016/12/08 ... e-grapher/
And one receives a weird result.
Still on the “filter frequency response grapher”, change b1 to -b1
One receives the correct graph
To follow that , the LPF calculation might simply be:
b1 = -exp(-2.0 * M_PI * Fc); // add minus
a0 = 1.0 + b1; //change minus to plus
According to the calculations, I adhere to this logic for LP:
b1 = -exp(-2.0 * 3.14 * Frequency);
a0 = 1.0 + b1;