- SoundCloud's new AAC encoder (Fraunhofer's libfdk_aac) removes frequencies above 17 kHz, unlike the old encoder, but improves overall audio quality.
- Lossy compression prioritizes what to discard to meet file size targets; the new encoder optimizes bitrate by cutting inaudible high frequencies, enhancing clarity in the audible range.
- Human hearing is most sensitive between 2-5 kHz and declines at higher frequencies, making frequencies above 17 kHz an efficient sacrifice for better mid-range accuracy.
- The encoder trades off barely perceptible high frequencies for cleaner mid-range signals, reducing errors and artifacts where listeners are most sensitive.
- Even at 256 kbps, the encoder applies a gentle rolloff at 17 kHz based on Fraunhofer's listening tests, prioritizing measurable improvements over full bandwidth.