Update docs audio (#1445)

* add information about spl rules to competition page

* add audio section

docs/robotics/perception/audio.md

@@ -0,0 +1,23 @@
+The NAO has four microphones, which are located in the head.
+They support frequencies between 100 and 10,000 Hz.
+
+For more details, have a look at the [documentation](http://doc.aldebaran.com/2-8/family/nao_technical/microphone_naov6.html) by Aldebaran.
+
+The audio cycler contains only two nodes, the microphone recorder and the whistle detection.
+
+## Microphone Recorder
+
+Reads the audio samples from the `MicrophoneInterface` and stores them in the audio cycler [database](../../framework/databases_and_types.md).
+
+## Whistle Detection
+
+Detects the whistle.
+Similar to regular soccer, the referee uses a whistle to signal the start and end of the game.
+More details on that can be found in the official [SPL rules](https://spl.robocup.org/wp-content/uploads/SPL-Rules-master.pdf)
+
+The whistle detection works (simplified) by comparing the average power of the audio samples withthin a certain frequency band by using the [FFT](https://en.wikipedia.org/wiki/Fast_Fourier_transform).
+This approach is not very advanced but works well in practice.
+
+!!! tip
+
+    The [Nao Devils](https://naodevils.de/) have put a lot of research into this topic and published datasets and [papers](https://naodevils.de/publications.html) regarding whistle detection and whistle localization.

docs/workflow/competition.md

@@ -59,3 +59,13 @@ For games, a strict schedule is created, which looks like this:
     Sometimes parameter changes are still made after this stage.
 -   30 minutes prior: Golden Goal <br>
     A kick-off against an empty field is performed. This is the final test before the game.
+
+## Game Rules
+
+Every team member should be familiar with the [SPL rules](https://spl.robocup.org/wp-content/uploads/SPL-Rules-master.pdf).
+
+Generally speaking, one goal of the SPL is to stay as close to the official soccer rules as possible, however, there are some key differences.
+
+!!! note
+
+    It's a good idea to read the rules before the competition, even if you are not refereeing yourself.