Added first-order HP and LP compensation filters to the biquad class

src/lasp/filter/biquad.py

@@ -23,7 +23,8 @@ y[n] = 1/ba[3] * (  ba[0] * x[n]   + ba[1] * x[n-1] + ba[2] * x[n-2] +
 
 """
 __all__ = ['peaking', 'biquadTF', 'notch', 'lowpass', 'highpass',
-           'highshelf', 'lowshelf', 'LPcompensator', 'HPcompensator']
+           'highshelf', 'lowshelf', 'LP1compensator', 'LP2compensator',
+           'HP1compensator', 'HP2compensator']
 
 from numpy import array, cos, pi, sin, sqrt
 from scipy.interpolate import interp1d
@@ -157,7 +158,32 @@ def lowshelf(fs, f0, Q, gain):
     a2 = (A+1) + (A-1)*cos(w0) - 2*sqrt(A)*alpha
     return array([b0/a0, b1/a0, b2/a0, a0/a0, a1/a0, a2/a0])
 
-def LPcompensator(fs, f0o, Qo, f0n, Qn):
+def LP1compensator(fs, f0o, f0n):
+    """
+    Shelving type filter that, when multiplied with a first-order low-pass 
+    filter, alters the response of that filter to a different first-order
+    low-pass filter.
+
+    Args:
+        fs: Sampling frequency [Hz]
+        f0o: Cut-off frequency of the original filter [Hz]        
+        f0n: Desired cut-off frequency [Hz]
+    """
+    
+    omg0o = 2*pi*f0o
+    omg0n = 2*pi*f0n
+    
+    z = -omg0o
+    p = -omg0n
+    k = p/z
+    
+    zd, pd, kd = bilinear_zpk(z, p, k, fs)
+
+    sos = zpk2sos(zd,pd,kd)
+    
+    return sos[0]
+
+def LP2compensator(fs, f0o, Qo, f0n, Qn):
     """
     Shelving type filter that, when multiplied with a second-order low-pass 
     filter, alters the response of that filter to a different second-order
@@ -194,7 +220,32 @@ def LPcompensator(fs, f0o, Qo, f0n, Qn):
     
     return sos[0]
 
-def HPcompensator(fs, f0o, Qo, f0n, Qn):
+def HP1compensator(fs, f0o, f0n):
+    """
+    Shelving type filter that, when multiplied with a first-order high-pass 
+    filter, alters the response of that filter to a different first-order
+    high-pass filter.
+
+    Args:
+        fs: Sampling frequency [Hz]
+        f0o: Cut-on frequency of the original filter [Hz]        
+        f0n: Desired cut-on frequency [Hz]
+    """
+    
+    omg0o = 2*pi*f0o
+    omg0n = 2*pi*f0n
+    
+    z = -omg0o
+    p = -omg0n
+    k = 1
+    
+    zd, pd, kd = bilinear_zpk(z, p, k, fs)
+
+    sos = zpk2sos(zd,pd,kd)
+    
+    return sos[0]
+
+def HP2compensator(fs, f0o, Qo, f0n, Qn):
     """
     Shelving type filter that, when multiplied with a second-order high-pass
     filter, alters the response of that filter to a different second-order