Audio

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 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.

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

The whistle detection works (simplified) by comparing the average power of the audio samples withthin a certain frequency band by using the FFT. This approach is not very advanced but works well in practice.

Tip

The Nao Devils have put a lot of research into this topic and published datasets and papers regarding whistle detection and whistle localization.