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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!

If you have already bought it, you can download the update from the download section of your Account page. If you haven’t, you can pick it up at my online shop!


a1Rotate


a3Rotate


a7Rotate

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

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Better Externalisation with Binaural

Some research that I was involved in was published last week in the Journal of the Audio Engineering Society [1]. You can download it from the JAES e-library here. The research was led by Etienne Hendrickx (currently at Université de Bretagne Occidentale) and was a follow on from other work we did together on head-tracking with dynamic binaural rendering [2, 3, 4].

The new study looked at externalisation (the perception that a sound played over headphones is emanating from the real work, not inside the listener’s head). It specifically investigated the worst case scenario for externalisation – sound sources directly in-front of ($0^{circ}$) or behind the listener ($180^{circ}$). It tested the benefit of listeners moving their head, as well as listeners keeping their head still and the binaural source following a “head movement-like” trajectory. Both were found to give some improvement to the perceived externalisation, with head movement providing the most improvement.

The fact that source movements can improve externalisation is important because we don’t always have head tracking systems. Most people will experience binaural with normal headphones. This hints at a direction for some “calibration” to help the listener get immersed in the scene, improving their overall experience.

Also importantly, the listeners used in the study were all new to listening to binaural content. This is important because lots of previous studies use expert listeners, but the vast majority of real-world listeners are not experts! The results of this paper are encouraging because they show that you don’t need hours of listening to binaural to benefit from some instant perceptual improvement in a fairly easy manner.

References

[1] E. Hendrickx, P. Stitt, J. Messonnier, J.-M. Lyzwa, B. F. Katz, and C. de Boishéraud, “Improvement of Externalization by Listener and Source Movement Using a ‘Binauralized’ Microphone Array,’” J. Audio Eng. Soc., vol. 65, no. 7, pp. 589–599, 2017. link

[2] E. Hendrickx, P. Stitt, J.-C. Messonnier, J.-M. Lyzwa, B. F. Katz, and C. de Boishéraud, “Influence of head tracking on the externalization of speech stimuli for non-individualized binaural synthesis,” J. Acoust. Soc. Am., vol. 141, no. 3, pp. 2011–2023, 2017. link

[3] P. Stitt, E. Hendrickx, J.-C. Messonnier, and B. F. G. Katz, “The Role of Head Tracking in Binaural Rendering,” in 29th Tonmeistertagung – VDT International Convention, 2016, pp. 1–5. link

[4] P. Stitt, E. Hendrickx, J.-C. Messonnier, and B. F. G. Katz, “The influence of head tracking latency on binaural rendering in simple and complex sound scenes,” in Audio Engineering Society Convention 140, 2016, pp. 1–8. link

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What Is… Spatial Audio?

This post is the first in a What Is… series. The idea is to explain different techniques, terminology and concepts related to spatial audio. This will range from the most common terms right through to some more obscure topics. And where better to start than “spatial audio” even means!

Spatial audio (with some exceptions) has generally been confined to academia but is rapidly finding applications in virtual reality (VR). There are even moves to bring it to broadcasting so it can be enjoyed by people in the comfort of their living rooms. As spatial audio moves from labs to living rooms it is worth exploring all of the different techniques that have been developed up to this point.

However, defining spatial audio can quickly become rather philosophical. For example, is a mono recording spatial audio? If I take a single microphone to a concert hall and record a performance then I have captured the sense of space, through echoes and reverberation, not just the performances themselves. This means that the space is encoded into the signal – we can tell if a recording is made in a dry studio or a cathedral. For the purposes of this series I will not be considering this to be spatial audio. Instead, I will be defining spatial audio as any audio encoding or rendering technique that allows for direction to be added to the source. How well this is reproduced to the listener will depend on the encoding and playback system but, in general, a spatial audio system will allow different sounds placed in different positions to be directionally differentiated.

There are a large number of different spatial audio techniques available and which one you want to use will depend on the final use. These techniques include (but are in no way limited to):

  • Stereophony
  • Vector Base Amplitude Panning (VBAP)
  • Ambisonics and Higher Order Ambisonics (HOA)
  • Binaural rendering (using HRTFs over headphones)
  • Wave Field Synthesis (WFS)
  • Loudspeaker diffusion
  • Discrete loudspeaker techniques

Each of these will be explained in more detail in future posts but you can see from this non-exhaustive list that there are already quite a few techniques to choose between. To further complicate things, some of these techniques can be combined in order to take advantage of different properties of both. For example, Ambisonics and binaural can be combined in VR and augmented reality (AR) to give a headphone-based rendering that can be easily rotated (a nice property of Ambisonics).

Spatial audio techniques can also be divided between those that aim to produce a physically accurate sound field in (at least some of) the listening area and those that are not concerned with matching a “real” sound field. HOA and WFS can both be used to recreate a holophonic sound scene using an array of loudspeakers. Meanwhile, stereo and VBAP do not recreate any target sound field but are still able to produce sounds in different directions.

Whether or not the spatial audio technique is physically-based or not, we also have to consider the potentially most important element in the whole chain: the listener! All of these techniques rely on how we perceive the sound and there are any number of confounding factors that can take our nicely defined (in a mathematical sense) system and throw many of our assumptions out the window. Therefore, this What Is… series will also include elements of spatial hearing and psychoacoustics that are essential to consider when working with spatial audio.

So, spatially audio can take a number of forms, each with their own advantage, disadvantages, limits and creative possibilities. It is these, along with the technical and psychoacoustic underpinnings, that I will expand upon in upcoming blog posts.

If there are any aspects of spatial audio that you’d like to have explained then leave a comment below.