ADAU1701 Audio Input Issues

Hello,

I have a problem with the sound input on my ADAU1701 DSP. I have a self-designed board and can successfully transfer programs to the dsp and they are executed without problems (e.g. a sine wave generator). However, if I just connect the inputs to the outputs I get no output. In my circuit I use 18kΩ input resistors. Has anyone been able to solve the same problem or can give me a hint what the problem could be?

With best regards,
olel