In a shelving equalizer, the frequency at which the equalizer begins to flatten out, or shelve. Defined as the frequency at which the level is 3 dB above (or below) the shelving level.
"Thanks for the amazing job you did on the collection of OLD 45's that I sent! They were not in very good condition with the numerous scratches. I had been hanging on to them for 35 years, so, was I ever pleased to be able to listen to them again without the scratches. Another shipment will be coming your way!! Thanks,"