denosing signal using wavedec and waverec

I am trying to use wavedec and waverec to denosing signals. suppose i have a signal x with some gaussian noise and then apply wavedec to do a level 3 db3 decomposition, i have two outputs, C and I, the wavelet decomposition vector C and the bookkeeping vector l, which contains the number of coefficients by level. Since we are doing a level 4 decomposition, I is a 4 by 1 vector. Assume the first two level manifest most noises, how do i threshold the coefficients in these two levels and then use the result for waverec?