Netflix revealed through a Tech Blog on its web site today that it has started improving the quality of audio delivered via its streamed programming.

The over-the-top content provider announced the availability of what it calls “high-quality audio,” defined as sound delivered at a higher audio bit rate for Dolby Atmos and 5.1 surround sound tracks.

Netflix said it is making the sound enhancements available for all movies and TV shows with 5.1 surround and Dolby Atmos. However, the service is continuing to deliver the higher quality audio formats in the lossy Dolby Digital Plus format and not Dolby’s lossless Dolby True HD format. Dolby uses either surround sound compression scheme to carry the extra Dolby Atmos information.

Netflix explained: “our high-quality sound feature is not lossless, but it is perceptually transparent. That means that while the audio is compressed, it is indistinguishable from the original source. 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. 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.”

Of course to get the most out of this new benefit, users should have a nice home theater audio setup, prepherably with a Dolby Atmos-decoding AV receiver and Atmos speaker package or an Atmos-supporting sound bar. But even if this is not available Netflix said: “We want your experience to be brilliant even if you aren’t listening with a state-of-the-art home theater system.”

The bit rate for 5.1 surround from these new “high-quality audio” tracks will increase from 192 Kbps to 640 Kbps, Netflix reported. On Dolby Atmos material — object-based sound with height channels and greater immersion — the bit rate will increase from 448 Kbps to 768 Kbps. In addition to having audio gear outfitted with a Dolby Atmos decoder, a subscription to the Netflix Premium Plan will be necessary to receive the premium Atmos enhanced audio content.

What does this greater bit rate do? According to the statement, Netflix is calling this high-quality audio because it “delivers audio that sounds closer to what creators hear in the studio, so every little detail is captured for a richer, more intense experience.”

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For those with bandwidth contraints or device limitations, Netflix said “we’ve made the feature adaptive so that we will deliver the best possible audio to match your capabilities. This is similar to what we already do for video.”

Netflix has used the so-called “adaptive streaming” technology in the past to send video over contrained broadband pipelines that vary in speed between peak- and low-use periods. Content may be down-rezed or have resolution restored as bandwidth opens up.

According to the blog, the impetus for the sound feature improvement came in 2017 while viewing its hit series Stranger Things 2, when the Netflix technical was able to get the lower-fi sound of a car chase scene to match more closely to the quality heard in the production studio by upping the bit rate for audio. After that, the company worked out a process to offer sound quality improvements more broadly.

By Greg Tarr

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