Doubling effect on LE7 eliminate HELP!

Hello I have cubase le7 with tad am 1800 interface. I’ve done a lot of YouTube watching and research trying to find out how to get rid of the doubling sound when recording my vocals when I’m using my headphones. I have the mix knob set to computer, when I turn it to input there is no sound . When I turn the dial knob on monitor back-and-forth, does not do nothing . The phones control is all the way up. I seen on full versions of 7 it offer a control room feature that apparently is not in LE7. This is driving me crazy of how to eliminate this when recording my vocals. Is there anyway to fix this in LE7 or do I have to go up to a full version to get this feature. If I can adjust something to get a dry sound on my recording vocal "please " someone help me. Again have my needing a full version of Cubase to have the control room picture to a limonite the doubling effect on vocals. Thanks anyone for your help !!!