The legend below Figure 17 says:

There are two Audio Elements (with audio_element_id = 11 and 12) which need to be mixed. The audio_element_id = 11 and the audio_element_id = 12 are linked to the Audio Element OBUs with audio_element_id = 11 and audio_element_id = 12, respectively.

I don't understand the sentence. It seems that it is saying 11 = 11 and 12 = 12?

I suggest removing the second sentence.