Yes of course, but that is a value relative to the signal S. In other words : THD= D/S and using dB expressions THD = D - S. What I was asking for was a tile of just the value of D and not its value relative to S (THD). It is a little like THD+N and N+D. THD+N is the component relative to the S signal of N+D. Of course, this is just a requirement of mine that perhaps no one cares about! 