is a high-quality, DRM-free digital audio format introduced by Apple for the iTunes Store. It features music encoded in 256 kbps AAC (Advanced Audio Coding), providing roughly double the bit rate and significantly better fidelity than the original 128 kbps protected format. Core Technical Features
On the night she published the Julian Voss collection, a former Apple iTunes engineer emailed her. “We called those ‘Plus files’ internally,” he wrote. “The AAC encoder we used had a psychoacoustic model tuned by a guy who later worked on hearing aids. He used to say: ‘256kbps is where the ear stops guessing.’ Julian reviewed that encoder. He said it made MP3s sound like photographs of fire. AAC was the fire itself.” Itunes Plus Aac M4a Sites
That someone was Elara.