{"id":12827,"date":"2020-05-29T15:21:23","date_gmt":"2020-05-29T15:21:23","guid":{"rendered":"https:\/\/dev01.contentcreators.at\/austrian-audio-ambicreator\/"},"modified":"2020-05-29T15:21:23","modified_gmt":"2020-05-29T15:21:23","slug":"austrian-audio-ambicreator","status":"publish","type":"post","link":"https:\/\/dev01.contentcreators.at\/de\/austrian-audio-ambicreator\/","title":{"rendered":"Austrian Audio AmbiCreator"},"content":{"rendered":"\n

AmbiCreator \u2013 producing Audio for VR and 360\u00b0 content with the OC818
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by Christoph Frank<\/p>\n\n\n\n

This is my second blog post for Austrian Audio, but this time it will not be about hardware development<\/a> but software instead.<\/p>\n\n\n\n

At this year\u2019s AES show we will release our new plugin, called the AmbiCreator, which can be used with a pair of OC818 microphones to create Audio for VR and 360\u00b0 videos.
We wanted to showcase it at the fair show together with our headphones, but as these are special times for all of us here is the \u201crelease show\u201d as a blog post.<\/p>\n\n\n\n

So, lights off, spots on\u2026<\/p>\n\n\n\n

What is ambisonic?<\/strong><\/h2>\n\n\n\n

When we talk about audio for VR and 360\u00b0 videos, we need to talk about ambisonics.<\/p>\n\n\n\n

There is a ton of information about ambisonics on the internet \u2013 and whereas scientific papers like e.g. in the AES archives show the great development in this field, most of what you find online is just copy and paste of the same graph showing the balloon plots of the different orders of ambisonics: I bet the graph comes as the first picture if you google ambisonics<\/a>.<\/p>\n\n\n\n

However, as I have the feeling that this doesn\u2019t help most people in the audio industry let me try to explain it in more hands-on audio terms.<\/p>\n\n\n\n

My dear friends Franz Zotter and Mathias Frank from the Institute of Electronic Music, IEM Graz, also wrote a great book where I can especially recommend the first chapter<\/a> \u2013 have a read, it\u2019s for free!<\/p>\n\n\n\n

As you probably already know, every polar pattern we normally use (figure-of-eight, cardioid, omni and everything in between) can be achieved by a combination of a figure-of-eight and an omni.
We also call this a mixture of the pressure (omni) and pressure-gradient (figure-of-eight) component.
This is actually also what you do when designing a microphone capsule \u2013 you try to achieve the appropriate combination of a \u201csealed\u201d capsule (omni) and an open \u201cfigure-of-eight\u201d capsule (where sound can also travel to the backside of the membrane) by finding the right acoustic resistance to balance them.
The directional characteristics, e.g. a cadioid pattern, we can achieve by this combination can only face in one direction \u2013 so a variation is only possible along one axis.<\/p>\n\n\n\n

David Josephson explains nicely how this is done for his  C700 series microphones here<\/a>.<\/p>\n\n\n\n

He also explains how a cardioid which can \u201clook\u201d around a full 360\u00b0 angle on the horizontal plane when two figure-of-eight patterns, angled 90\u00b0 towards each other, are combined with an omni characteristic.<\/p>\n\n\n\n

Shoeps\u2019 Double-M\/S microphone and plugin also uses this approach although here the second figure-of-eight and the omni are already superseded by two cardioids – so three microphones in total.<\/p>\n\n\n\n

If we now bring in a third figure-of-eight pattern to the equation, we can actually calculate a cardioid which can \u201clook\u201d around in every angle both on the horizontal and vertical plane or any combination.<\/p>\n\n\n\n

Spoiler-Alarm: Below you can see how a Super-Cardioid calculated via our new AmbiCreator Plugin \u201clooks\u201d around a full circle in the vertical plane.<\/p>\n\n\n\n

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And now we get to the point where, damn, even I also need to re-post the famous ambisonics graph (with permission from Mathis Frank \u2013 no, we are not related, he\u2019s far more clever than me\u2026)<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

Figure from Ambisonics<\/em>, Franz Zotter and Matthias Frank, Springer Verlag (2019)<\/p>\n\n\n\n

The first row shows and omni characteristic, which is referred as zero order ambisonics.
The second row is the 1st<\/sup> order ambisonics with the three figure-of-eight patterns all along a different axis. Together with the omni we can generate all the patterns we are used to like super-,hyper- and wide-cardiod which are referred as 1st<\/sup> order patterns.<\/p>\n\n\n\n

The other two rows shown are 2nd<\/sup> and 3rd<\/sup> order ambisonics which basically make narrower characteristics than cardioid possible to achieve better localisation, more on that later. For these you need special microphone arrays where companies like Zylia kick in, go here. <\/a><\/p>\n\n\n\n

Is ambisonics the same as binaural \/ 8D audio?<\/strong><\/h2>\n\n\n\n

There is a hype going on lately called \u201c8D\u201d \u2013 it stands for 8 Dimensions and has this certain \u201cwow\u201d effect when you listen to it on headphones. And this is the point \u2013 it works on headphones and headphones only, the same is true for binaural audio.<\/p>\n\n\n\n

Both are essentially stereo files where audio was either recorded or rendered with HRTFs<\/a> to achieve an extremely realistic localisation and immersive (damn, now I also said the i-word\u2026) experience.
These HRTFs are actually different for each individual, so how well this works depends if your ear fits to the artificial head which was used for recording or the HRTFs which were used for processing the 8D music to give the impression as if a certain sound is coming from a specific direction.
But they mostly fit well enough end yield in an impressive result.<\/p>\n\n\n\n

However, coming back to the initial question \u2013 NO, this has nothing to do with ambisonics!<\/p>\n\n\n\n

A 1st<\/sup> order ambisonics audio stream, which is also the 3D audio definition available within youtube, is basically a 4 channel file containing the signals of the bespoke trio of figure-of-eight and the omni pattern.
Imagine you really use such 4 microphones to record in the middle of an essemble, the ambisonics audio file would simply be those 4 raw tracks \u2013 this is called B-format.<\/p>\n\n\n\n

This file on its own is relatively useless \u2013 you will need a certain de-coder to get material for our usual playback setups out of it, which are:<\/p>\n\n\n\n

Stereo:<\/strong> a simple X\/Y stereophony signal could be calculated from a B-format stream\u2026
Surround:<\/strong> Signals for 5.1, 7.1 or any other horizontal speaker configuration can be calculated out of it<\/p>\n\n\n\n

These two would only use the two figure-of-eight patterns in the horizontal plane<\/p>\n\n\n\n

If we also use the vertical figure-of-eight, newer audio formats can be the output of a B-format decoder, like<\/p>\n\n\n\n

Surround including height channels: <\/strong>speaker setups like 11.2 (which is 7.1 with a second subwoofer and 4 height channels above the listener) can be calculated out of it
Binaural:<\/strong> with a certain set of HRTFs, a binaural stereo signal for playback on headphones can be calculated<\/p>\n\n\n\n

Wait \u2013 didn\u2019t I just say binaural has nothing to do with ambisonics?<\/strong><\/h2>\n\n\n\n

Yes, because binaural is just one of the many \u201coutput-formats\u201d we can gain from an ambisonic-stream. For this, a bunch of directional patterns (mostly super- or hyper-cardioids) facing in a certain set of angles are calculated \u2013 then these signals are processed with the correspondent HRTF for this direction and summed up to one stereo file.
More sophisticated binaural encoders use some tricks to improve localisation (like the one developed by the IEM<\/a> which I recommend) \u2013 however, the localisation can never be as good as a true binaural recoding as the 1st<\/sup> order patterns are rather broad.<\/p>\n\n\n\n

On the other hand, if you listen to a true binaural recording (like the famous virtual barber shop<\/a> and you turn your head, nothing will change as this is a static recording.
But if you en-code an ambisonics stream to binaural, the sound sources will move with the rotation as they can be recalculated in real time if you have some sort of head tracking available. The nice thing is that we have all such a device in our pocket!
A mobile phone has several gyro sensors and a compass inside and can do that processing for you.<\/p>\n\n\n\n

So a true binaural recoding can\u2019t be used for VR or 360\u00b0 videos as the sound cannot move with the viewer looking around.<\/p>\n\n\n\n

A-format vs. B-format<\/strong><\/h2>\n\n\n\n

If you ever looked up for ambisonic microphones, you will have probably read about A-format rather than B-format.<\/p>\n\n\n\n

This is because a microphone array consisting of three figure-of-eight capsules and one omni is rather hard to realise, so the alternative is a microphone consisting of 4 cardioid capsules where all our needed patterns can be superseded by those.
Besides these special A-format microphones (starting at around 1000\u20ac), you will need a plugin which calculated the B-format stream out of the A-format signal and voila \u2013 you have your ambisonics signal commonly accepted by most DAWs and platforms like Youtube.<\/p>\n\n\n\n

Shouldn\u2019t this be a release show rather than a scientific monologue?<\/strong><\/h2>\n\n\n\n

Okay \u2013 now I told you everything I know about ambisonics (don\u2019t forget to read this book<\/a> to REALLY know about ambisonics) we get to the fun part \u2013 recoding ambisonics with our OC818 microphones.<\/p>\n\n\n\n

As you know, all our OC818 microphones are calibrated to have the exact same sensitivity, which make them ideal for stereo recordings. With our PolarDesigner plugin, you can even experiment with different polar patterns in post-production to find the best stereo setup for your recording.<\/p>\n\n\n\n

With our newest plugin AmbiCreator we go one step further \u2013 getting an ambisonic B-format signal out of two OC818 microphones, e.g. a Live-Set.<\/p>\n\n\n\n

As our OC818 microphones have a dual output, we can calculate any 1st<\/sup> order pattern (now you know what the scientific chitchat was good for) from those two outputs.
If you really read so far, you will already know that we need three figure-of-eight patterns and the omni signal for this.<\/p>\n\n\n\n

Omni and figure-of-eight in the horizontal are easy and no need to explain, right? But what about the figure-of-eight in the vertical direction?<\/p>\n\n\n\n

Well, we use a \u201ctrick\u201d here which relates to the very common endfire beamforming technique used in telecom and automotive.<\/a><\/p>\n\n\n\n

Thomas, our plugin programmer, and I wrote an eBrief for the AES show which you can read here<\/a>, if you want to know the details. It will basically tell you how this is achieved and show that the vertical axis \u201conly\u201d works up two around 2kHz \u2013 however as most of music\u2019s and voice\u2019s content is in this range, it actually works quite well for all recoding situations!<\/p>\n\n\n\n

To demonstrate the effect, we did some test recordings with some of Vienna\u2019s finest musicians and a drummer (Sorry Walter for that joke!) in the Porgy&Bess jazz club.<\/p>\n\n\n\n

This nice location gave us the possibility to place the musicians also at an vertical angle (e.g. the great Ulrich Drechsler<\/a> was placed on the balcony far behind the recording rig) \u2013 further, they were also \u201copen\u201d during these difficult times as they are hosting their great \u201cthe show must go (on)line\u201d<\/a> series of streamed live performances. Make sure to check it out and leave them a tip every Thursday and Saturday!<\/p>\n\n\n\n

The two OC818 microphones were placed on top of each other close to the 360\u00b0 camera \u2013 no additional microphones were used, instruments were balanced by moving musicians back and forth (old-school techniques meet 21st<\/sup> century technologies if you will). Besides the plugin-processing, no additional EQ or effects were used.<\/p>\n\n\n\n

\"\"<\/figure>\n\n\n\n

So if you have some sort of VR-glasses (even google cardboard works fine) and a pair of headphones, here are our first two recordings:<\/p>\n\n\n\n

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