While AAC uses SBR to reconstruct high frequencies, SONE214 employs a machine-learning-driven "spectral prediction network." Instead of guessing high-frequency content, the decoder uses a lightweight neural net trained on millions of music tracks to re-synthesize lost harmonics. The result? A 128 kbps SONE214 file can sound indistinguishable from a 320 kbps MP3, even on high-end monitor speakers.
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