Here's what I found
To use an aggregate device with Logic:
Open Logic Pro or Logic Express.
Choose Logic Pro > Preferences > Audio or Logic Express > Preferences > Audio and select the Devices tab.
Select the Output Device drop-down menu and choose the aggregate device from the list. ...
Click Apply Changes at the bottom-right of the window.
To capture a certain size frame of the persons face mainly to emphasize on who is talking
Greater than or eaqual to 3. By the way this is the wrong place to ask a math question. Next time mark the question in mathematics not computer science. They are two different subjects.
google or search through pvps