Hello, yes I visited the page. I toke the example as reference. Firstly I used unsigned long but then I changed to int. Newbie error! 
I have to read out only one analog input (one microphone). (Now I commented it out in my sketch). So the theoretically maximum sampling rate is 8.333Hz (1.000.000us/120us). Many thanks for your example! I need some time to understand. Than hopefully we will see how much time it needs to call the filters.