The existence of "Ecco the Dolphin" had been heavily rumored throughout the industry before it was finally revealed by Sega in 1992 as a Genesis exclusive, then simply known as "Dolphin". After deciding to create a game based around dolphins, developer Ed Annunziata carried out research on the subject and was particularly inspired by the book "Sounding" by Hank Searls which explained how the creatures use echolocation. Annunziata worked with the music team on the soundtrack, playing them songs by Pink Floyd to illustrate the feeling he was aiming for. Annunziata later said: "I was paranoid about game rentals and kids beating the game over the weekend. So... I... uh... made it hard". His favourite level was "Welcome to the Machine", which was "way over the top challenging".