The PERCH spectral simulator is based on quantum mechanical calculation. One can define different line-width for each nucleus. Large spin-systems are packed using X-approximation.  

This allows, for example, simulation of cyclosporine A spectrum (89 protons, 56 particles) and with X-approximation also much larger spin-networks like testosterone (28 fully coupled protons).

Note: Starting with version 2011.1 even huge structures like Glucagon (MW: 3519.210 | MF: C153H225N43O49S) can be predicted and simulated.