Noise Shaping
Definition
A dithering technique that redistributes quantization noise from the most audible frequency range (2–4 kHz, where human hearing is most sensitive) to less audible frequencies (typically above 15 kHz). Applied during bit-depth reduction to make the added dither noise less perceptible.
In Simple Terms
A smarter version of dither that pushes the noise into frequencies your ears are less sensitive to. When converting from 24-bit to 16-bit, noise shaping makes the unavoidable dither noise virtually inaudible by hiding it in the upper frequencies where you're less likely to notice it.
In Practice
When mastering to 16-bit for CD delivery, the engineer selects a noise-shaping dither algorithm (such as POW-r Type 3) that pushes quantization noise above 14 kHz, making it inaudible on most playback systems while preserving low-level detail in the critical midrange.