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A stereo audio recording is captured using two microphones to capture sounds simultaneously. The mono signals from each microphone are assigned to the left or right channel. The stereo effect is achieved through the slight variation in the sound between the left and right channels. By placing the microphones at slightly different locations, the recorded sound will arrive at the microphone at a slightly different time and at different levels. A difference in just a few milliseconds is enough to create the illusion of width and space absent in mono recording.
Listening to stereo audio comes from two fixed positions from either the left or right channels. In this scenario, if you take out your left earbud, you will only hear sound mapped to the right position. If you are not using headphones, you must be equally distant from the right and left speakers, as your placement within a room relative to the speakers will affect stereo imaging. Obviously this all gets more complex with the number of speakers and their placement around the room, plus the acoustics of that room.
Listening to binaural audio places you center-stage at the orchestra. In this scenario, sound is positioned in a 360-degree space around you. However, binaural recordings sound the same no matter where your head is positioned. It really only makes sense to listen to a binaural audio recording with headphones to replicate a specific listening experience.
Today, more and more applications and games are benefitting from spatial audio. The use cases are boundless, from social chat apps and immersive games to live streaming events and virtual reality experiences.
The BBC has used spatial audio to record the BBC Proms, Doctor Who and the Turning Forest VR fairy tale. It can be used as part of 360 video, standard video or radio. This guide is to help producers explore how to use spatial audio in their productions.
Spatial audio is so similar to what we hear in real life, it has the potential to immerse the listener more fully than standard audio. BBC Academy technology trainer, John Heraty, demonstrates. Put your headphones on.
A microphone with four cardioid microphones pointed in different directions - a tetrahedral shape. It requires a software-based decoder to convert the front-back, up-down, left-right signals. Various models are available.
Initial start-up costs can be as low as 85 for in-ear mics to 1,500 for higher-end mics. Good mics with free software plug-ins may appear cheaper but require good digital audio workstations and are not as effective as purchased software.
If you use professional binaural microphones you will be limited in what you can alter in post-production. This means you'll need to spend more time recording to get performances and atmos that work together. The binaural head shown here cost 6,500.
If you use mono mics, the sound can be processed in post using software-generated synthetic binuaural. Audio can be panned and artificial rooms created. This requires specialist software and studio time. Practise using free plug-ins.
To experiment it's easiest to start with binaural sound. You can capture spatial audio using simple in-ear mics. Little can be changed in post-production but you can create good effects using free software plug-ins which can be used with most digital audio workstations and will allow steering of mono sounds around the listener.
To include spatial audio in a future programme, object-based audio is the best solution. Object-based audio involves capturing sound using mono mics that are moved in space during post-production. BBC R&D is developing standards for object-based audio files. These will be future-proofed and can be re-purposed for any platform.
You can now stream multi-channel Dolby Atmos 7.1.4 audio to your iPhone or iPad, and apply Apple Spatial binaural rendering to the received stream, allowing you to hear how your Dolby Atmos content will on Apple Music.
Technology to emulate this natural experience anywhere has been a pursuit for well over a century. In 1881, a French engineer named Clement Ader invented the Thtrophone, which used 80 telephone transmitters connected across the stage of the Paris Opera. These transmitters created a binaural stereoscopic sound (a method of recording sound with two microphones arranged to replicate the 3D stereo sound one perceives in real life). With this, appreciators of the opera could listen from as far away as two kilometers.
About 30 years later, in 1972, Neumann released their first commercial binaural recording system, allowing the replication of spatial sound to be simplified and consistent across various applications. Technology and methods have since improved, including a newer technique of using arrays instead of just two distinct microphones to get a more detailed recording of a given space.
Today, advanced audio techniques are being integrated in all sorts of audio applications (from music to gaming) on all sorts of devices like sound bars, headphones, TWS earbuds, automobiles, and XR devices.
The earliest form of this was stereo sound, with two speakers, then into quad sound with 4 speakers. This advanced to surround sound, with 5.1, 7.1 (where there are 5 and 7 speakers, respectively, and a single subwoofer for lower frequencies), and large speaker arrays (way more than 7) for more spatial output.
While 5.1 and 7.1 surround sound systems emulated sound around you, it was only really in a single plane around you as those speakers surround you at about the same height. Dolby Atmos has come into the audio space to give audio cues of sounds above and below you, creating a more immersive experience.
Similarly, sounds should stay in place in the world even after motion. The gif below shows the difference between binaural audio and head tracked binaural audio. When you rotate your head, the world should not rotate with you, it should stay in place.
2. when I'm bouncing directly from the normal "bounce" section' i can see that I have the option to choose surround. When it comes with that option, I can see that the file is muti channel, at 7.1.4 format, so if I want to deliver that file to my client for uploading to apple music or other publishing that requires true surround file, this is how I need to do that? Or do I need to export it as an ADM BWF file?
3. when using the Binaural mode, I can see that it's stereo, compared to the 7.1.4 file multi-channel. What is the difference between them? The Binaural is "emulating" the surrounding environment compared to the 7.1.4 that split the multi-channels for multi outputs? So that means that spatial audio will work on any normal headphones, and when I want to listen to the 7.1.4 file, I need to use the Apple Airpods Pro/Max, and it will translate the file into a surround?
5. I did some tests with 7.1.4,5.1 and binaural, then I bounced it and tried to open from my cloud in my iPhone, I can see that the audio is multi-channel, but I can't hear any difference between the rear (ear level) and the rear top. Only on the binaural can I hear a difference between the ear and top levels. Why is that?
1. The monitoring format selected in the Dolby Atmos plug-in does not affect the surround format when you export your Dolby Atmos mix to an ADM BWF file: the exported mix is a 7.1.4 Dolby Atmos compatible file.
3. When monitoring in Binaural mode the surround content is downmixed to a stereo signal, authentically replicating the spatial placement of audio cues as experienced in the original multichannel content. Binaural content can be played on any headphones.
4. Dolby Atmos will play on any headphones. AirPods (3rd generation), AirPods Pro, and AirPods Max support spatial audio and dynamic head tracking. Spatial audio is not required for Dolby Atmos playback.
1. so, if I understand, I can mix in Binaural mode and then deliver to my client the 7.1.4 file, and it will work as it should? And what happens if I use panning above ear level and bounce it for 5.1? that will translate to ear level, or it will be gone?
5. so I can't hear true surround file from my iPhone with my Airpods Pro, correct? or I need a specific app, or otherwise can I hear that from my mac when I connect my AirPods? or only from the Apple Music app?
That's one of the big selling points of Dolby Atmos: no need for mixing engineer to deliver multiple formats for different playback system. One single format (ADM BWF) can be played back on playback system of any format.
Encoding and creating the MP4 file requires a Dolby encoding solution. Both the Dolby Atmos Renderer and Dolby Media Encoder applications can process ADM BWF files created by Logic Pro. Simply open the ADM BWF file and export the audio as an MP4 with the Music encoding mode.
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