diff --git a/docs/changelog.rst b/docs/changelog.rst
index 31dea2b..1129935 100644
--- a/docs/changelog.rst
+++ b/docs/changelog.rst
@@ -1,8 +1,9 @@
 ChangeLog
 =========
 v0.1.9
+------
 * New features:
-    * Add `audioflux.utils.synth_f0`
+    * Add `audioflux.utils.synth_f0`.
 * Fix bug:
     * `#37 <https://github.com/libAudioFlux/audioFlux/issues/37>`__: Fix `audioflux.display.fill_spec` bug.
 
diff --git a/python/audioflux/utils/util.py b/python/audioflux/utils/util.py
index 874713e..24c52ae 100644
--- a/python/audioflux/utils/util.py
+++ b/python/audioflux/utils/util.py
@@ -139,6 +139,7 @@ def synth_f0(times, frequencies, samplate, amplitudes=None):
     Examples
     --------
 
+    >>> import audioflux as af
     >>> import numpy as np
     >>> f0_arr = np.ones((1024,)) * 220
     >>> times = np.arange(0, f0_arr.shape[0]) * (1024 / 32000)