Second harmonic distortion (HD2): Ratio of second-order harmonic to the input signal (carrier). Often measured as dBc.
"Thanks for the great job in transferring one of my prized pipe organ recordings to CD! All around, a very well-done job – the finished CD sounds spectacular and, not having a turntable anymore, it was great to hear this outstanding recording once again! I’m planning to send several cassette tapes along for transfer soon!"