o·ver·dub 
(ōvər-dŭb′)
(ōvər-dŭb′)tr.v. o·ver·dubbed, o·ver·dub·bing, o·ver·dubs
To add (supplementary recorded sound) to a previously taped musical recording especially in order to heighten the total effect.
n.
Additional recorded sound that is blended into a musical recording: instrumental overdubs.