Audio App for mix input from external audio card starts with sound even if the getNextAudioBlock() is empty

Hi, I’m making an audio app to start and mix the inputs from an external audio card, but even if in the getNextAudioBlock() I have nothing, the card outputs the first two input channels (the card ias a Presonus AudioBoc 1818VSL).
How can I prevent this?

Are you calling AudioSourceChannelInfo::clearActiveBufferRegion to actually clear any audio in the buffer passed to you in getNextAudioBlock()?