‘High quality audio’ reduces compression to 'nearly lossless' levels

Netflix is upgrading its audio settings to provide quality as close to the original program master.

The network says the changes were prompted by input from the Duffer brothers, producers of its wildly popular “Stranger Things” series. The producers noted audio degradation in the second season in 2017, which spurred Netflix to revisit the networks’ entire audio chain with the goal of reproducing audio quality as close to what producers intended.

“Series mixes were getting bolder and more cinematic with tight levels between dialog, music and effects elements,” Netflix said in a blog. “Creative choices increasingly tested the limits of our encoding quality. We needed to support these choices better.”

Since inception, Netflix has used static audio streaming at a constant bitrate, which “selects the audio bitrate based on network conditions at the start of playback,” according to the company. For video, however, Netflix has used adaptive streaming that optimizes video quality based on the viewers’ network connection.

So Netflix decided to carry the adaptive streaming concept to audio by developing an algorithm that allowed the technology to be supported and certified by the myriad streaming devices used to access its service.

“Based on internal listening tests, listening test results provided by Dolby, and scientific studies, we determined that for Dolby Digital Plus at and above 640 kbps, the audio coding quality is perceptually transparent,” Netflix said. “Beyond that, we would be sending you files that have a higher bitrate (and take up more bandwidth) without bringing any additional value to the listening experience.”

It also adopted what it terms a “bitrate ladder” for 5.1-channel audio ranging from 192 up to 640 kbps. This ranges from “good” audio to “transparent,” according to Netflix.

For Dolby Atmos, the company increased the bitrates on its highest offerings to 768 kbps. “We expect these bitrates to evolve over time as we get more efficient with our encoding techniques,” the company said.

More information is available here