diff --git a/content/zettels/digital_filters.md b/content/zettels/digital_filters.md
new file mode 100644
index 0000000..3c56dfa
--- /dev/null
+++ b/content/zettels/digital_filters.md
@@ -0,0 +1,12 @@
++++
+title = "Digital Filters"
+author = ["Thomas Dehaeze"]
+draft = false
++++
+
+Tags
+:
+
+A nice open access book on digital filter is accessible here: <https://ccrma.stanford.edu/~jos/filters/filters.html>
+
+<./biblio/references.bib>
diff --git a/content/zettels/irr_and_fir_filters.md b/content/zettels/irr_and_fir_filters.md
index c69cc19..fa2042f 100644
--- a/content/zettels/irr_and_fir_filters.md
+++ b/content/zettels/irr_and_fir_filters.md
@@ -5,7 +5,7 @@ draft = false
 +++
 
 Tags
-:
+: [Digital Filters]({{< relref "digital_filters" >}})
 
 <div class="table-caption">
   <span class="table-number">Table 1</span>:
@@ -32,7 +32,7 @@ Tags
 >
 > The primary disadvantage of FIR filters is that they often require a much higher filter order than IIR filters to achieve a given level of performance. Correspondingly, the delay of these filters is often much greater than for an equal performance IIR filter.
 
-From ([Shaw and Srinivasan 1990](#org5be9a82))
+From ([Shaw and Srinivasan 1990](#org9a58282))
 
 > The FIR are capable of realizing filters with linear phase shift characteristics and furthermore are less susceptible to signal input and filter coefficient quantization effects.
 > However, their computational demands are excessively large because of the large number of multiplications and additions to be performed at each sampling interval.
@@ -51,4 +51,4 @@ From <https://dsp.stackexchange.com/a/30999>
 
 ## Bibliography {#bibliography}
 
-<a id="org5be9a82"></a>Shaw, F.R., and K. Srinivasan. 1990. “Bandwidth Enhancement of Position Measurements Using Measured Acceleration.” _Mechanical Systems and Signal Processing_ 4 (1):23–38. <https://doi.org/10.1016/0888-3270(90)>90038-m.
+<a id="org9a58282"></a>Shaw, F.R., and K. Srinivasan. 1990. “Bandwidth Enhancement of Position Measurements Using Measured Acceleration.” _Mechanical Systems and Signal Processing_ 4 (1):23–38. <https://doi.org/10.1016/0888-3270(90)>90038-m.