Princess Anika and the Sound Sapphires
Once upon a time, in a magical land, there were three kingdoms. The first was called Equestria, and was filled with magical, friendly, and adventurous ponies. The second was the Crystal Empire, a crystal-y kingdom in the icy north, with Earth crystal ponies, that helped spread love and light across the lands. The third was the Sound Kingdom, which maintained sound in the land, and filled with very powerful unicorns who helped animals and objects make sound. This story is about the third, the Sound Kingdom.
Long ago, before the events of Heart's Warming Eve, a group of mortal alicorns started a kingdom in the faraway mountainous region of what is now known as Equestria. They were the ancestors of the King Harmony and Queen Melody. They had gathered very powerful unicorns into their kingdom, built walls up, and had protected the entire land.
There was a special magical school for young unicorns that taught the most difficult types of magic, and how to create sounds. The unicorn foals would eventually work at the castle or magical stables, taking care of animals or maintaining sound.
They also had worked long and hard to capture at least two of every creature, keeping them in comfortable pens to begin making sounds and noises for each and every creature. After generations of perfections and mistakes, they'd successfully made appropriate noises for them. They then did the same with all inanimate objects.
But like all kingdoms and empires, it had an enemy or two to fight off. The most dangerous and powerful of these was the evil and corrupt Ear Splitter. She was a princess who had been banished from the kingdom after being caught tampering with all the backup sounds. She had vowed revenge on her "traitorous" relatives, and had eventually been banished into the Sound Dimension.
The Sound Dimension was a dimension filled with Sounds of Mistakes, all of the tossed and imperfect noises that the unicorns and alicorns of the Sound Kingdom had given up on, and believed they could never be fixed.
And so the Sound Kingdom kept itself secret and impenetrable, access only open to a select few. They kept hidden their secret weapon-the Sound Sapphires!