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## 50% Discount on aXPanner and aXMonitor

Today I’m having April sale and putting a 50% discount on my Ambisonic panning and decoding plugins for Windows (VST) and MacOS (VST/AU): aXPanner and aXMonitor. This offer runs until the 30th April 2018.

The aXPanner converts mono and stereo signals to YouTube360 compatible AmbiX-format Ambisonics. The aXMonitor decodes these Ambisonic signals to two-channel stereo and binaural (3D audio over headphones) formats to allow easy monitoring. Together they form the essential signal chain for spatial audio and are a great way to get started with Ambisonics.

You can check out my short tutorial on getting started with a basic Ambisonics chain here.

The aXPanner and aXMonitor available for three levels of spatial resolution: first, third and seventh order Ambisonics. Higher orders increases the spatial fidelity of the sound scene.

This 50% discount can be combined with additional 20% bundle discounts for additional savings.

You can read more details about them in my web store :

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The o1Panner is dead. Long live a1Panner!

My first plugin release was a free first order encoder called the o1Panner. Today it gets an update to version 1.0.1 and a new name. Here is a list of the updates:

• name change from o1Panner to a1Panner to match the naming convention of the rest of the aX Ambisonic Plugins.
• Unifies the colour scheme with the rest of the a1 Ambisonic Plugins.
• Removes the JUCE splash screen on first open of the plugin during a session.
• Now available as an AudioUnit on Mac.
• 32 bit Windows version available.
• Mac VST and AU are now Universal Binary.

So, no changes to the features, just added flexibility to where you can use it.

And no changes to the price – it’s still free!

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## aXMonitor Update: Google Resonance Audio HRTFs

• The HRTFs used for binaural 3D sound have been regenerated using Google’s own Resonance Audio toolkit for VR audio. These are the same HRTFs used by Google in YouTube 360. The code released by Google is only up to 5th order, but was actually quite simple to extend to 7th order.
• A gain control has been added to boost or cut the overall level for convenience.

The minor update is a fix to make sure the plugin reports the correct latency to the host when using the Binaural or UHJ Super Stereo (FIR) methods.

Google have just open sourced their Resonance Audio SDK, including all sorts of tools for spatial audio rendering. This update to ensures that you can aXMonitor ensures that you can mix your content on HRTFs that will be widely used across the industry.

The aXMonitor is available in 3 versions, providing up to first, third and seventh order Ambisonics-to-binaural decoding.

So if you’d like to start mixing your VR/AR/MR audio content just head over to my store. With your support, I can continue to update the aX Ambisonics Plugins to bring you the tools you want and need.

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## aXRotate Update to v1.2.0: Now With Head Tracking!

The aXRotate plugin receives an update today to version 1.2.0 and it’s a big one!  What’s more, it now comes as a (Universal Binary) AudioUnit format for Mac!

Version 1.0.0 was a plain vanilla Ambisonics rotation with yaw, pitch and roll control. Version 1.2.0 adds two new features that massively increase its usefulness:

• Get head tracking by connect an EDTracker module.
• Increase the spaciousness of your static binaural mixes by adding micro oscillations to the sound scene.

Let’s go into both of these new features in a bit more detail.

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## Product Spotlight: aXCompressor

The aXCompressor is a compressor VST plugin (Windows and Mac) made specifically for Ambisonics signals. It comes in three variations: first order (a1), third order (a3) and seventh order (a7), allowing you to process . They accept any Ambisonics format that has the W channel as the first channel. This means it works for the more modern AmbiX and legacy FuMa format.

There are plenty of Ambisonics encoders and decoders but not so many things to process between these two points on the signal chain. I wanted to help bring some of the tools we take for granted when working in stereo to VR/AR and immersive audio, hence the aX Plugins. If you’re interested in trying out any of the plugins, including the aXCompressor, you can download the demo versions. You can support future development by making a purchase at from my web shop.

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## Introducing the aX Ambisonics Plugins

Today I am very happy to be releasing my latest work: the aX Ambisonics plugins. They are the result of a lot of work and it is great to be able to finally release them into the world.

The aX Plugins are a set of VST plugins intended to make your work with spatial and immersive audio that little bit easier. They come in three variations each with equivalent plugins – a1, a3 and a7.

Which one you choose will depend on the level of spatial resolution you need for your project (how accurately the spatial properties are reproduced to the final listener). The different levels are known in the Ambisonics world as the order and can theoretically go to infinity. In practice we can (thankfully!) stop somewhere quite a bit before infinity! The aX Plugins give you a choice between basic, advanced and future-proof version.

What are the plugins and what can they do?

There are currently seven plugins in each suite with a different purpose. Here is a quick summary:

1. aXPanner – a stereo to Ambisonics encoder to bring your sounds into the spatial domain.
2. aXRotate – this plugin will let you rotate a single track or a full sound scene to make sure you have everything exactly where you want it.
3. aXMonitor – Ambisonics needs a decoder to be listened to. This plugin decodes to binaural 3D audio (over headphones) or to standard stereo. This means you can always share your creativity via traditional channels.
4. aXCompressor – Ambisonics requires careful handling of the audio to avoid changing the spatial balance. aXCompressor lets you compress the signal without alteration.
5. aXGate – simiarly, this plugin acts as a noise gate and downwards expander while preserving the spatial fidelity.
6. aXEqualizer – safely sculpt the tone of your signals.
7. aXDelay – get creative with five independent delay modules that can be rotated independently of the original signal.

I will be doing a series of posts going into more detail about each plugin. You can also get more information on the product pages. In the meantime, if you are curious, you can download demo versions of these plugins (for evaluation purposes only) here and if you like them you can support future development by buying them from the shop. Thanks!

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## What’s Missing From Your 3D Sound Toolbox?

Audio for VR/AR is getting a lot of attention these days, now that people are realising how essential good spatial audio is for an immersive experience. But we still don’t have as many tools as are available for stereo. Not even close!

This is because Ambisonics has to handled carefully when processing in order to keep the correct spatial effect – even a small phase change between channels significantly alter the spatial effect – so there are very few plugins that can be used after the sound has been encoded.

To avoid this problem we can apply effects and processing before spatial encoding, but then we are restricted in what we can do and how we can place it. It is also not an option if you are using an Ambisonics microphone (such as the SoundField, Tetra Mic or AMBEO VR), because it is already encoded! We need to be able to process Ambisonics channels directly without destroying the spatial effect.

So, what is missing from your 3D sound toolbox? Is there a plugin that you would reach for in stereo that doesn’t exist for spatial audio? Maybe you want to take advantage of the additional spatial dimensions but don’t have a tool to help you do that. Whatever you need, I am interested in hearing about it. I have a number of plugins that will be available soon that will fulfil some technical and creative requirements, but there can always be more! In fact, I’ve already released the first one for free. I am particularly interested in creative tools that would be applied after encoding but before decoding.

With that in mind, I am asking what you would like to see that doesn’t exist. If you are the first person to suggest an idea (either via the form or in the comments) and I am able to make it into a plugin then you’ll get a free copy! There is plenty of work to do to get spatial audio tools to the level of stereo but, with your help, I want to make a start.

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## Free Ambisonics Plugin: o1Panner

I am working on some spatial audio plugins to provide some more tools for VR/AR audio and I am kicking things off with a freebie: the o1Panner. It is free to download from the Shop.

### What is it?

The o1Panner a simple first-order Ambisonics encoder with a width control.

### How to use it

There are two display types: top-down and rectangular. The azimuth, elevation and width are controlled in different ways in each of these views. The views are selected by right clicking on the display.

For the top-down view, azimuth is controlled by clicking and dragging on the main display, the elevation is controlled by holding shift and dragging up/down and width is controlled by holding ctrl and dragging up/down.

For the rectangular view, azimuth and elevation correspond to the x- and y-coordinates respectively and width is controlled by holding ctrl and dragging up/down.

### What does it output?

The output is AmbiX (SN3D/ACN) Ambisonics. This is the format used by Google for YouTube 360 and is quickly being adopted as the standard for Ambisonics and HOA.

### What’s coming up?

I am working on several Ambisonics and HOA plugins that will be available in 2018. Some of them will do things that other plugins do, but most of them should do something new. Some of them will do something more creative and experimental. If you want to see a certain effect for spatial audio, just get in touch and let me know what you want. If you’re the first person to suggest a plugin that gets developed then you will get a free copy to say thanks!

The industry is rapidly moving on from first-order Ambisonics and embracing HOA. For example, ProTools recently added support up to third-order Ambisonics. Higher order tools are in the pipeline, so check back soon.

### Stay Up To Date

If you want to keep current with upcoming plugin news and about updates to the o1Panner, subscribe to the mailing list:

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## Ambisonics to Stereo Comparison

In my last post I detailed two methods of converting Ambisonics to stereo. Equations and graphs are all very good, but there’s nothing better than being able to listen and compare for yourself when it comes to spatial audio.

With that in mind, I’ve made a video comparing different first-order Ambisonics to stereo decoding methods. I used some (work-in-progress) VST plugins I’m working on for the encoding and decoding. I recommend watching the video with the highest quality setting to best hear the difference between the decoders.

There are 4 different decoders:

• Cardioid decoder (mid-side decoding)
• UHJ (IIR) – UHJ stereo decoding implemented with an infinite impulse response filter.
• UHJ (FIR) – UHJ stereo decoding using a finite impulse response filter.
• Binaural – Using the Google HRTF.

The cardioid decoder more quickly moves to, and sticks in, the left and right channels as the source moves, while this is more gradual with the UHJ decoder. To me, the UHJ decoding is much smoother than the cardioid, making it perhaps a bit easier to get a nice left-right distribution that uses all of the space, while cardioid leads to some bunching at the extremes.

The binaural has more externalisation but pretty significant colouration changes compared to UHJ and cardioid decoding, but also potentially allows some perception of height, which the others don’t.

The VSTs in the video are part of a set I’ve been working on that should be available some time in 2018. If you’re interested in getting updates about when they’re release, sign up here:

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## Ambisonics Over Stereo

Ambisonics, especially Higher Order Ambisonics, is great for 3D sound applications. But what if you have spent a long time mixing for a 3D audio format but want to share it with listeners who are only listening on stereo?

The first thing depends if they’re going to be using headphones or loudspeakers. If they’re using headphones then you can create a binaural mix in the usual way. If they are using loudspeakers then binaural is no longer an option (unless you want to go down the fragile transaural route). In this post we will focus on how you can decode from first order Ambisonics to stereo using one of two common options.

## Mid-Side Decoding

The first option is probably the simplest – treat the Ambisonics signal as a mid-side recorded scene by taking the W and Y channels, with W being the mid and Y being the side. Then you can make your left and right (L and R) stereo playback channels using \begin{eqnarray} L = 0.5(W+Y),\\ R = 0.5(W-Y) \end{eqnarray}

This is effectively the same as recording a sound field with two cardioid microphones pointing directly left and right. Sounds panned to 90 degrees will play only through the left loudspeaker and those at -90 degrees through the right.

The advantage of this sort of decoding is that it is very conceptually simple and, as long as your DAW can handle the routing, it is even possible to do without any dedicated plugins. It also results in pure amplitude panning, meaning that it has all of the advantages and disadvantages of standard intensity-stereo. However, we’ve got another option to choose from when we want to play back over a stereo system that has some advantages.

## UHJ Stereo

A more complex and interesting technique is UHJ. We’re only going to go over how UHJ for stereo listening, but it is worth noting that UHJ is mono compatible and that a 4-channel version exists from which full first-order Ambisonics information that can be retrieved via correct decoding. 3-channel UHJ can get you a 2D (horizontal) decoder by retrieving the W, X and Y channels. A nice property of the 3- and 4-channel versions is that they contain the stereo L and R channels as a subset. This means, importantly, 2-channel UHJ does not require a decoder when played back over two loudspeakers. All you need to do is take the first two channels of the audio stream.

The stereo L and R channels can be calculated using the following equations:\begin{eqnarray} \Sigma &=& 0.9397W + 0.1856X \\ \Delta &=& j(-0.3430W + 0.5099X) + 0.6555Y\\ L &=& 0.5(\Sigma + \Delta)\\R &=& 0.5(\Sigma – \Delta)\end{eqnarray} where $$j$$ is a 90 degree phase shift.

You can see from these equations, converting to UHJ from first-order Ambisonics results in signals with phase differences between the L and R channels. This creates quite a different impression to the kind of mid-side decoding mentioned above. There will obviously be some room for personal taste as to whether or not UHJ is actually preferred to mid-side decoding. Sound sources placed to the rear of the listener are more diffuse when reproduced of a stereo arrangement than those at the front, while for mid-side decoding there is no sonic distinction between a sound panned to 30 degrees or to 150 degrees.

Beyond front-back distinction, UHJ can actually result in some sounds appearing to originate from outside the loudspeaker pair by a small amount. This is why it is sometimes referred to as Super Stereo. In my experience, this effect is very dependent on the sound being played, both its frequency content and how transient it is.

Because UHJ stereo relies on phase differences between the two channels, any post-processing or mastering applied should preserve the phase relationship between L and R, otherwise there is a very real risk that the final presentation will be phase-y and spatially blurred.

Figure 1 shows the localisation curves for a sound played back over a stereo system where the signal in the Ambisonics domain is panned fully round the listener. Obviously the sound stays to the front, but the actual trajectories between UHJ and mid-side decoding are quite different. (These localisation curves were calculated using the energy vector model of localisation, so they are most appropriate for mid/high frequencies and broadband sounds).

Which of the two stereo loudspeaker decoding strategies you’ll want to use will depend on the needs of your project. Mid-side decoding is simpler and results in pure amplitude panning. UHJ can result in images outside of the loudspeaker base, but relies on the phase information being preserved. If you want to retrieve any spatial information then UHJ is absolutely the way to go.

## Tools for Stereo Decoding

I have an old Ambisonics to UHJ transcoder VST that you can download here, but they are old and I am not sure how compatible they are with newer version of Windows and Mac OSX. To remedy that, I’ve been working on an updated version that will provide simple first-order to stereo decoding. Just select which method you want to use and pump some Ambisonics through it. Keep an eye out in the near future for when it is made available!

I’m curious to hear from anyone who has used both techniques what you prefer. Leave a comment below!