diff --git a/ChangeLog b/ChangeLog
index 3c3a08f6fd..5dd6f8f3b2 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,8 @@
+2007-06-20  Stefan Kost  <ensonic@users.sf.net>
+
+	* gst/equalizer/gstiirequalizer.c:
+	  Document parameter mapping.
+
 2007-06-20  Stefan Kost  <ensonic@users.sf.net>
 
 	* gst/spectrum/gstspectrum.c: (gst_spectrum_event),
diff --git a/gst/equalizer/gstiirequalizer.c b/gst/equalizer/gstiirequalizer.c
index 926b1e0a6b..ff11c9e713 100644
--- a/gst/equalizer/gstiirequalizer.c
+++ b/gst/equalizer/gstiirequalizer.c
@@ -311,9 +311,17 @@ gst_iir_equalizer_finalize (GObject * object)
   G_OBJECT_CLASS (parent_class)->finalize (object);
 }
 
-/* args are in the range [-1 ... 1] with 0 meaning "no action"
- * convert to [-0.2 ... 1] with 0 meaning no action via the function
- * f(x) = 0.25 * 5 ^ x - 0.25
+/*
+ * converts gain values to scale factors.
+ *
+ * arguments are in the range [-1 ... 1] with 0 meaning "no action"
+ * results are in the range [-0.2 ... 1] with 0 meaning "no action"
+ * via the function
+ *   f(x) = 0.25 * 5 ^ x - 0.25
+ *
+ * visualize via gnuplot:
+ *   set xrange [-1:1]
+ *   plot 0.25 * exp (log (5) * x) - 0.25
  */
 static gdouble
 arg_to_scale (gdouble arg)