Guitar Hero II

I have all GH games after Guiter Hero 1 and sometimes I have problems with the lag on my TV. I just recently got GH2 and I CANNOT get the lag right. Could someone please explain how the lag works?

Here's what I think I know:
-I can't get my lag right because it won't let me go into the negative settings, like on rockband.
-Audio and video settings are independent of when you should actually hit the notes... meaning that thereis a specific time when you should strum that doesn't go by when you see or hear the notes.
-To have an effective lag calibrating system, they should let us be able to adjust audio and video both for positive or negative settings, like rockband.

The further I move my video setting into the positive, the worse the lag gets for GH2 and audio is unadjustable.
Is there anyway I could adjust the lag outside of the game, like with some kind of device or something because it's pretty much impossible for me to 5* songs like rock this town when I can 5* every song on GH3 with my wii.