def biquad2(w_num, r_num, w_den, r_den):
b = np.array([<NUM_LIT:1>, -<NUM_LIT:2>*r_num*np.cos(w_num), r_num**<NUM_LIT:2>])<EOL>a = np.array([<NUM_LIT:1>, -<NUM_LIT:2>*r_den*np.cos(w_den), r_den**<NUM_LIT:2>])<EOL>return b, a<EOL>
A biquadratic filter in terms of conjugate pole and zero pairs.

Parameters
----------
w_num : zero frequency (angle) in rad/sample
r_num : conjugate zeros radius
w_den : pole frequency (angle) in rad/sample
r_den : conjugate poles radius; less than 1 for stability

Returns
-------
b : ndarray of numerator coefficients
a : ndarray of denominator coefficients

Examples
--------
>>> b,a = biquad2(pi/4., 1, pi/4., 0.95)