The sound effects used for SEGA's 3DS homescreen themes were created with authentic recordings.
SEGA producer Yosuke Okunari recently tweeted some images taken during the production of these themes, which include recording genuine sounds used in the UI of the Dreamcast and SG-1000.
He noted that the team wanted to "recreated the short 'Buu' sound when turning on the console for the SG-1000 theme so we brought the console for recording." The sound, however, does vary depending on the software running, so the group needed to "start up roughly 20 games and choose the one which sounded most authentic."
Have you downloaded the new SEGA 3DS themes?