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AMBEO audio streaming on Netflix
AMBEO experience now streaming on Netflix
NIGEL JOPSON explains how Sennheiser adds exciting sound for viewers without the need for a surround system
Netflix and Sennheiser have announced a significant audio improvement for all viewers accessing the popular streaming service: AMBEO 2-channel Spatial Audio is now implemented on Netflix, and delivers an enhanced immersive audio experience to viewers with standard speakers. Full control of the amount of spatialisation on immersive audio objects is set by the re-recording mixer.
“Most people watching Netflix are listening on the speakers built-in to their devices,” Scott Kramer, manager for sound technology at Netflix, told me. I wondered if earbuds and headphones might be significant for tablet or mobile devices, but Kramer told me: “headphones are a pretty small percentage, so AMBEO worked better than binaural for us because it works well on speakers. For a Netflix spatial audio feature, we look at any technology that meaningfully improves the sound experience for members. This includes binaural encoding that happens on mobile devices, and speaker based ‘transaural’ technologies.”
An imperative for Netflix was to respect creative intent and engage with production pros involved with mixing audio for picture. “We want to adopt sound technologies which keep the re-recording mixer involved in determining the result, and which have a clean sound that’s respectful of the mix,” Kramer emphasised. “It’s also important to cover the most members possible without regard to what device they use. For this, pre-encoded solutions are a clear fit.”
While in the past those viewers without a full surround sound set-up were unable to benefit from the growing amount of music and films produced in Dolby Atmos® or MPEG-H Audio, the AMBEO 2-Channel Spatial Audio feature aims to change this. Netflix’s Stranger Things Season 4 benefits from this new audio experience; currently 32 Netflix titles are available with AMBEO technology, and it’s growing on a daily basis.
Sennheiser ProLabs
I spoke to Dr. Renato Pellegrini, manager of Swiss-based Sennheiser ProLabs, to discover more. “We work on projects for all Sennheiser business units, including Neumann and Dear Reality, and I am in very close contact with the newly acquired Merging Technologies,” Pellegrini told me. “We help each other — we’ll find out what will make sense for a given customer base as an upcoming product; we share our thoughts and inputs from users to come up with next generation solutions.”
ProLabs’ brief to deliver a spatial sound for viewers, without the need for a surround system, was to develop a set of tools for re-recording mixers. These tools would take an original immersive mix — let’s say a Dolby Atmos mix or an
We take object based input — so the rerecording mixer may choose the amount of effect that is wanted
/ The preview tool of the AMBEO 2-Channel Spatial Audio rendering software. The Object
Viewer window at the bottom right shows fixed loudspeaker positions at the edges and individual renderings as blue dots. Pale dots are elevated sound sources / From standard stereo mixdown (left) to full AMBEO effect (right): mixers can fine-tune the spatialisation
MPEG H mix — and create a two channel version far better than the normal stereo downmix. “We imagine this as a service that just runs in the encoding cloud,” explained Pellegrini. “As it’s currently deployed, there’s a tool that allows re-recording mixers to preview Dolby ADM [Audio Definition Model] files, to see and adjust the type of spatialisation. Then the ADM files can be processed, or the IAB [Immersive Audio Bitstream, the SMPTE interoperable solution] file can be processed in the streaming platform’s cloud, just like they would process any other ADM file, to deliver two channels.”
Mixing tools
A preview tool enables the re-recording mixer to compare stereo to AMBEO during postproduction and adjust the rendering settings by stems/groups. The renderer offers patented granular control of the spatialisation, ranging from full AMBEO effect to standard stereo mixdown, while specific channels can be excluded from any modification.
“We have a tool where mixers can actually pre-listen during their studio work” Pellegrini explains. “Mark Paterson, who mixed Stranger Things for instance, did the Atmos mix first, and at the point where the 5.1 downmix was done, he used our tools to listen to the two-channel outputs. Not much extra time is required to create a mix, and further time can be saved by relying on just the cloud mixer to do its trick.”
Re-Recording Mixer Mark Paterson commented: “I’m a huge fan of AMBEO. I experimented with it a lot on the Fear Street movies and was impressed with how the surround channel information was represented. I’m always looking for ways to get that cinematic sound at home, and on The Adam Project I was able to make the mix sound really immersive on everything from high-end soundbars to iPhones, which I believe helps the audience connect more emotionally. It’s been a perfect format on Stranger Things. In the Atmos mix, Vecna’s [the fearsome antagonist in season 4] voice wraps around you, which is an important part of making him scary and larger than life. The fact that AMBEO is able to help recreate that in stereo is very impressive to me.”
Object control
We asked Dr. Pellegrini how much control an Atmos re-recording mixer would have over the beds and objects which are included in an ADM file as
/ Mark Paterson, Stranger Things re-recording mixer
separate tracks. “We have a total of up to 128 mono files, which are grouped into groups that you have in your original Dolby Atmos mix”, he revealed. “Normally mixers would work in groups that they labelled very similar to the stems in their mix. So that would be dialogue, music, FX and so on. You can choose the amount of effect from the AMBEO pre-processing: a mix engineer might choose a little less on dialogue, not so much on music but a lot on the effects and the dramatic sounds — the aural ‘ambience’ that you want to create in the movie.”
Total loudness is preserved too, and a music mix can be kept clean for left and right channels while adding the immersive AMBEO rendering to other channels. All signals are properly timealigned to match the original content. “The processing is in line with Sennheiser’s reputation to deliver tools that are ‘transparent’ and do not interfere with the original sound. In a nutshell: Sennheiser 2-Channel Spatial Audio seeks to translate mixer intent, not to overpower it.”
Cloud processing
Rendering deliverables in AMBEO is not a process confined to the studio. “In the cloud, we have a different set of options,” Pellegrini continues. “The reason for having a cloud solution is simply that OTT players [Over-The-Top: provision of TV and film content over the internet at the request of the individual consumer] see a benefit in doing this type of conversion in the cloud.” All that requires to be done is to upload to the cloud an ADM or an IAB file, and then perform re-renders into the various formats within the cloud, on their servers. The benefit of this is to limit upload bandwidth, and to significantly reduce the work needed if there are multiple dubbed versions of the audio in different languages.
A template for the degree of spatialisation on different objects is pre-set by an accompanying control file. “The input of the parameters for cloud rendering is a simple XML file,” Pellegrini adds, “where you have the ability (on your command line in the cloud) to set all the parameters that you would have in the studio with the GUI version.” In other words, a re-recording mixer can set their parameters on the preview tool, save it as a file and send it alongside the ADM file for use with a range of deliverables.
Streaming Stranger Things 4
No additional upgrades to a viewer’s streaming account are required to experience the Netflix AMBEO spatial audio. Viewers can access content with AMBEO processing by searching for “spatial audio” in the Netflix app. It’ll be available first with original titles such as Stranger Things 4, The Witcher and Red Notice. As long as the user’s device audio output is set to stereo audio, they won’t have to adjust any settings to try AMBEO. Netflix is making it the default setting for two-channel setups for certain titles.
“There is some difference in how our technology works as opposed to other offerings in the market,” Pellegrini explains, as he adds that Sennheiser will likely be open to negotiate deals with other big players in the streaming market in future. “Not only do we take object based input, but also we deliver very granular control — so the re-recording mixer may choose the amount of effect that is wanted. It’s patented technology by Sennheiser, and it’s something that the customer base — from producers to mixers — really love because it’s not just an ‘on-off’.”
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