https://www.cnet.com/news/netflix-now-sounds-better-when-you-watch-it/

To address the issue, the show was streamed at a higher bitrate that sounded closer to what the original studio master did. This laid the groundwork for Netflix to create its new high-quality audio feature.

High-quality audio not only delivers a higher bitrate but can adapt to the speed of your internet connection by increasing or decreasing that bitrate. Netflix video already does something similar. If you've ever been on a slower connection, you have probably seen a video playback at a lower quality until there's enough of a buffer for it to switch to a higher quality version. High-quality audio will do the same and move up and down in quality seamlessly as you watch a show.