Higher order filters

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Re: Higher order filters

Post by steve » Sun Jun 18, 2017 10:39 pm

Here's an 8th order 10000 Hz low pass filter based on cascading biquad filters with Q values from this page: http://www.earlevel.com/main/2016/09/29 ... g-filters/ and biquad parameters from this page: http://www.earlevel.com/main/2013/10/13 ... ulator-v2/

Code: Select all

(setf b0 0.21683529588969896)
(setf b1 0.43367059177939793)
(setf b2 0.21683529588969896)
(setf a0 1.0)
(setf a1 -0.14770935819940134)
(setf a2 0.015050541758197231)
(setf *track* (biquad-m *track* b0 b1 b2 a0 a1 a2))

(setf b0 0.23441015370614224)
(setf b1 0.4688203074122845)
(setf b2 0.23441015370614224)
(setf a0 1.0)
(setf a1 -0.15968144492938235)
(setf a2 0.09732205975395142)
(setf *track* (biquad-m *track* b0 b1 b2 a0 a1 a2))

(setf b0 0.2757000746652961)
(setf b1 0.5514001493305922)
(setf b2 0.2757000746652961)
(setf a0 1.0)
(setf a1 -0.18780835895394715)
(setf a2 0.29060865761513177)
(setf *track* (biquad-m *track* b0 b1 b2 a0 a1 a2))

(setf b0 0.3581186053323747)
(setf b1 0.7162372106647494)
(setf b2 0.3581186053323747)
(setf a0 1.0)
(setf a1 -0.24395230091976342)
(setf a2 0.6764267222492621)
(biquad-m *track* b0 b1 b2 a0 a1 a2)
and this is the effect on a 100 to 20000 Hz chirp with constant (0.8) level:
firsttrack000.png (8.95 KiB) Viewed 894 times
and this is the spectrum of filtered white noise:
window-Frequency Analysis-000.png
window-Frequency Analysis-000.png (39.95 KiB) Viewed 894 times
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