"It's a Harmonian Sonic Converter," the pretty woman with crystalline features who is selling the Rhapsodian novelties replies in a delightfully musical voice, "It can transform background noise into beautiful music or soothing sounds, like the sound of the ocean, or birdsong. It's a rare treasure of Rhapsodia, made of special crystals. I have some other amazing things from my home planet to share with you as well! For instance, these earrings are made from a special crystal that transforms very nearby soundwaves to a particular frequency, unique to the crystal that was used to make the earrings, and reverse-transforms any soundwaves from that special frequency back to their normal frequency and amplifies them, retaining high sound quality from a great distance. But why does it matter, you ask? Well, if you have more than one set of earrings made from the exact same crystal and wear one, you can whisper very softly and be heard across a room by the person to whom you give the other pair."