A second common problem in NMR spectroscopy is homonuclear decoupling of adjacent C spins, for example in 1 H, C correlation spectra of uniformly C-labelled biomolecules. Such couplings give rise to a cosine modulation, cos(πJt), in the free-induction decay (FID), which leads to broadening or a resolved multiplet structure. As for molecular weight, a variety of approaches have been developed to address this problem: isotopic labelling schemes that eliminate adjacent C nuclei ; band selective decoupling (although this is only effective for a subset of residues) ; virtual decoupling by computational deconvolution ; and constant time evolution, which while effective entails a substantial reduction in sensitivity .