Merge branch '122-clock-jitter-noise-should-saturate-below-around-1e-4-hz-2' into 'master'

Resolve "Clock jitter noise should saturate below around 1E- 4 Hz"

Closes #122

See merge request !155

lisainstrument/noises.py

@@ -80,7 +80,8 @@ def violet(fs, size, asd):
     Args:
         fs: sampling frequency [Hz]
         size: number of samples [samples]
-        asd: amplitude spectral density [/sqrt(Hz)]"""
+        asd: amplitude spectral density [/sqrt(Hz)]
+    """
     logger.debug("Generating violet noise (fs=%s Hz, size=%s, asd=%s)", fs, size, asd)
     if not asd:
         logger.debug("Vanishing power spectral density, bypassing noise generation")
@@ -89,18 +90,20 @@ def violet(fs, size, asd):
     return np.gradient(white_noise, 1 / fs) / (2 * pi)
 
 
-def pink(fs, size, asd):
+def pink(fs, size, asd, fmin=None):
     """Generate a pink noise in f^(-1/2) in amplitude.
 
     Args:
         fs: sampling frequency [Hz]
         size: number of samples [samples]
-        asd: amplitude spectral density [/sqrt(Hz)]"""
+        asd: amplitude spectral density [/sqrt(Hz)]
+        fmin: saturation frequency (default to fs / size) [Hz]
+    """
     logger.debug("Generating pink noise (fs=%s Hz, size=%s, asd=%s)", fs, size, asd)
     if not asd:
         logger.debug("Vanishing power spectral density, bypassing noise generation")
         return 0
-    generator = pyplnoise.PinkNoise(fs, fs / size, fs / 2)
+    generator = pyplnoise.PinkNoise(fs, fmin or fs / size, fs / 2)
     return asd / sqrt(2) * generator.get_series(size)
 
 
@@ -110,7 +113,8 @@ def red(fs, size, asd):
     Args:
         fs: sampling frequency [Hz]
         size: number of samples [samples]
-        asd: amplitude spectral density [/sqrt(Hz)]"""
+        asd: amplitude spectral density [/sqrt(Hz)]
+    """
     logger.debug("Generating red noise (fs=%s Hz, size=%s, asd=%s)", fs, size, asd)
     if not asd:
         logger.debug("Vanishing power spectral density, bypassing noise generation")
@@ -125,7 +129,8 @@ def infrared(fs, size, asd):
     Args:
         fs: sampling frequency [Hz]
         size: number of samples [samples]
-        asd: amplitude spectral density [/sqrt(Hz)]"""
+        asd: amplitude spectral density [/sqrt(Hz)]
+    """
     logger.debug("Generating infrared noise (fs=%s Hz, size=%s, asd=%s)", fs, size, asd)
     if not asd:
         logger.debug("Vanishing power spectral density, bypassing noise generation")
@@ -173,11 +178,14 @@ def clock(fs, size, asd):
 
         S_q(f) [ffd] = (asd)^2 f^(-1)
 
+    Clock noise saturates below 1E-5 Hz, as the low-frequency part is modeled by
+    deterministing clock drifts.
+
     Args:
         asd: amplitude spectral density [/sqrt(Hz)]
     """
     logger.debug("Generating clock noise fluctuations (fs=%s Hz, size=%s, asd=%s /sqrt(Hz))", fs, size, asd)
-    return pink(fs, size, asd)
+    return pink(fs, size, asd, fmin=1E-5)
 
 
 def modulation(fs, size, asd):