An optimization procedure is described for NMR techniques that require signal averaging of expts. with a variable time delay ti, either for the suppression of artifacts or for the optimization of coherence transfer over a given frequency range. The procedure is applied to 2-dimensional (2D) exchange spectroscopy, where artifacts due to zero-quantum coherence evolving in the mixing period (J cross peaks) can be canceled by co-addn. of signals from expts. with a refocusing pulse inserted at suitably chosen points in the mixing interval. Expts. must be averaged over a sizeable no. of ti values to obtain satisfactory cancellation. Suppression schemes may fail in systems with >2 spins if 2 or more of the chem. shifts are nearly degenerate. [on SciFinder (R)]