The age of immersive music production has begun and is noticeably picking up speed. Around 75% of the Apple Music Top 100 Global Charts are already available in Dolby Atmos and even numerous catalog releases are gradually being transferred to modern formats. In parallel, supply and demand for XR applications and metaverse experiences are increasing, also increasingly demanding musical 3D content. Fortunately, the necessary tools are becoming easier and more accessible, the distribution and playback challenges that 3D audio creators have faced in recent years have begun to fall, and as a result, more and more musicians and producers are inclined to finally express their creativity in all three dimensions.
To exploit the full potential of 3D audio, it is advisable to consider the possibilities of the larger stage already during production and recording. For example, it can be interesting to place elements behind or above the listening position, which sometimes has a clear influence on the arrangement of a piece. Also, from a sound perspective, instead of a one-dimensional axis (stereo), the move to immersive sound formats has given us 2 spatial axes at once, and thus significantly more “canvas” on which our music can take place. With this post, I’d like to leave mixing aside and instead give you some guidance on how to record a musical event in 3D.
By the way: If you don’t have an immersive speaker setup at your disposal, all formats (Dolby Atmos, Sony 360 RA, Auro 3D, Ambisonics, etc.) can actually be listened to binaurally on standard headphones.
Direct microphones
Just because we’re producing an immersive piece of music, of course doesn’t mean we’re throwing everything overboard we have learned so far! On the contrary, a three-dimensional mix provides more than enough space to freely place mono signals in the room. This means that all your favorite microphones and techniques can of course still be used. It is up to you whether you want to place your mono sources in the mix as objects or assign them to a bed, and you can also freely determine the size of the sound source in 3D space.
Sound producers have for a long time used more distant microphone positions in addition to close miking of the individual instruments (groups) in order to capture the diffuse sound of the room. Such distributed room microphones can also be understood as mono spots and distributed as desired in the three-dimensional space of the mix, so nothing changes very much in this respect. However, those who produce in 3D find that it is sometimes possible to accommodate many such spots in an immersive mix in order to capture a realistic and tangible spatiality. By the way, this does not mean that the arrangement in the room has to correspond to the arrangement in the mix; you actually have a lot of freedom in this regard. For room microphones, the general rule is that the more indirect the sound image, the better. By the way, with an abundance of 3D room spots, even cheap microphones can be used, because sound quality doesn’t really matter here, it is the mass that creates the immersive effect with this technique.
However, various mono microphones are of course best complemented in a 3D production by stereo, surround, and 3D miking, so we will cover these below.
Stereo miking
Stereo miking should also be familiar to most readers, as it has been an important basis for recording for decades and is used, for example, as main or room miking or directly on the instrument. There are stereo arrangements based on delay differences (e.g. AB), others that make use of the level differences between two directional microphone capsules (e.g. XY), those that combine both (e.g. ORTF) and even those that work with physical barriers between the microphones (e.g. dummy head).
Anyone who has used stereo miking up to now is of course welcome to stick with the tried-and-tested arrangements and place them as desired in the 3D mix. However, 3D audio additionally enables a new way of thinking about stereo miking through the additional spatial axes. The height axis in particular offers a completely new creative way of using stereo: You only have to rotate the array by 90° to record the top-bottom axis instead of the right-left axis.
Instruments that naturally have a pronounced height axis, on which several elements of the sound are to be found, such as double bass or cello, are particularly well suited for this. But also a fiddle, saxophone or flute performance can get a completely new liveliness and plasticity by stereo-miking the height axis. Keep in mind that “upright stereophony” may cause floor and ceiling reflections to play a greater role.
Surround miking
Surround arrays have so far been used rather rarely in music production and were more at home in film and film music contexts, concert recordings and the like. However, 3D audio naturally includes surround content that does not have a height axis by itself. Surround recording techniques capture, with relatively little effort, a very useful two-dimensional spatial signal that provides a super foundation for an immersive sound mix. Just as with mono and stereo, these can be augmented in the mix with treble components if needed.
Basically, any surround microphone system will work for your 3D production – and there are quite a few! For example, I can recommend the IRT Cross to install a quadrophonic base in a relatively small space. Also a good choice for “small kit” is the Double MS arrangement, which gets by with just three microphones and an extended MS matrix. Especially for large halls and lineups, however, you should definitely try a Hamasaki Square or even a Decca Tree with surround outriggers, because the large distance between the microphones and the resulting delay differences make for a very pleasant and natural sounding envelope.
Whether you’re working with a surround setup for 4.0, 5.0, or even 7.1, you can simply place the resulting signals directly on the designated channels of the bed, or choose a more flexible arrangement in the form of objects. Surround arrays are great for main or room miking.
3D miking
Over the years, sound engineers have come up with many microphone arrays that also include the third spatial axis. In most cases, this is a further development of an already known surround or stereo arrangement. Examples of this are ORTF-3D, ESMA-3D, or the Hamasaki Cube. All of these arrangements do a good job and the sound character of the arrays is comparable to their stereo and surround equivalents, which makes it relatively easy for experienced sound engineers to assess the sound aesthetics and use the arrays in a targeted way.
However, 3D arrays have logistical disadvantages, because usually 8 identical microphones with very high build quality and low tolerances are needed, which of course results in high cost. In addition, it takes quite a while to build and measure these arrays, especially when longer distances are involved (such as with Hamasaki). However, smaller arrays such as ORTF-3D can be transported as a fixed installation in a wind basket.
Ambisonics microphones
Ambisonic microphones are ready-made 3D microphone arrays. They are available in different orders, which are associated with different numbers of channels and have different spatial resolutions. First-order ambisonics (FOA), for example, has 4 channels, while third-order ambisonics already requires 16 channels.
The precisely calibrated capsules point in different directions and record the complete 3D sphere equally. After recording, conversion to B-format is usually necessary first, after which the “direction of view” and directivity of the microphone can be freely determined in post-production. The matrixing is relatively complex due to the higher number of capsules, but anyone familiar with the way an MS matrix works can think of Ambisonics as a big sister to it.
The elegant thing about Ambisonics is not only the complete 360° recording, but also the fact that you can convert Ambisonics signals into any speaker arrangement. For example, if you want to embed an Ambisonics signal in a Dolby Atmos mix, you can do so as a 7.1.2 bed or in the form of any number of individual objects (these then act as virtual speakers, so to speak).
By the way, particularly impressive results can be achieved by combining several Ambisonics microphones. For example, you can build a kind of three-dimensional AB miking from 2 Ambisonics microphones, with each of the two microphones responsible for one hemisphere. This combines three-dimensional imaging with the sonic benefits of time-of-flight stereophony. Another example is a 6DoF (“6 degrees of freedom”) array – this is a setup of many identical Ambisonics microphones, assembled by a digital software matrix to create an interactive 3D audio scene that allows the listener to move freely through the scenery.
Conclusion
Whether you want to release your next song as a binaural 3D version, in Dolby Atmos or Sony 360RA, or whether you’re working on a new VR game or the next Metaverse experience: the audio future is three-dimensional, and it pays to consider this already during production. I hope this article gives you some useful starting points and ideas for your next production and wish you much fun trying it out!
Do you have any experiences with 3D recording, tips or even questions about the topic? Share your thoughts in the comments!
