A new fashion has recently appeared, that of 8D music, that is 8-dimensional music that is depopulating almost everywhere, on youtube, on social media and so on.
We would like to clarify that immediately 8D is a misnomer used in this context since in addition to 3 spatial dimensions (in which it is actually possible to place the sound) and wanting to add another one (the temporal one) we would arrive at a maximum of four dimensions and not eight.
Unless of course some psychoactive substance has been used, dimensions of that order can in fact be experienced only in altered and higher states of consciousness and awareness, such as in mystical ecstasies, so much so that in some spiritual traditions as well as in times in quantum physics, we speak of an eleven-dimensional universe (11 dimensions in its entirety).
Returning to us, the technologies aimed at conferring spatiality to the sound, and to allow its positioning in the three-dimensional space have existed for many years, with subsequent updates and evolutions compared to the first formats, as it happens for all technological processes.
These technologies have been developed above all in the film and videogame field, in fact they arise from the desire to recreate a sound perception experience that is close to the real one with sounds coming from different spatial directions.
The first example to mention is the famous system "surround“, Developed in the film industry in the years 70: after several experiments, the standardization of a sound fruition system was achieved three channels frontal (Left, Front e Right) and a posterior channel (Surround Channel). In essence, spectators could hear the sounds coming from the screen as well as from speakers placed behind them, used above all for special sound effects. This is the DolbyStereo which has contributed to making films such as the famous one spectacular Star Wars. Over the years, "consumer" versions have been created for a home use of surround sound, and as the technology has evolved, adding an ever increasing number of channels for an ever more "immersive", enveloping and realistic perception of sound.
In this context, the Dolby Atmos, one of the most recent technologies developed in the field of cinema, which provides sound sources also coming from above (from the ceiling) thus introducing a vertical dimension of sound. Those just mentioned are all technologies that fall within the so-called multichannel audio, or they are made up of several distinct information flows, each of which represents a different sound channel (intended to be reproduced by specific loudspeakers).
The Dolby Atmos system however, unlike previous systems, is based on sound objects, each with its own characteristics, and each of which can be assigned a position in three-dimensional space.
What we want to deepen today, however, is a different type of technology, which does not require complex systems (consisting of decoders, a large number of loudspeakers, etc.), which is usable simply by using a pair of (good) stereo headphones.
It is of 'binaural audio: in practice the sound signal is treated by acting on those properties (acoustic, spatial, temporal) that allow our hearing, in the real world, to localize the sounds around us. So let's quickly see what are the mechanisms through which the human auditory system is able to recognize the origin of sounds.
Our organism is a wonderful system, capable of incredible things, which we often take for granted, and the auditory system is no exception. In practice, our auditory system is able to compare the physical characteristics of the sound that reaches the two ears and to obtain, from this comparison, information on the position of the source that generated it.
First of all it is able to calculate the difference in the times of arrival of the sound to the two ears, which is called ITD (acronym of English Interaural Time Difference). For example, if the sound source is on my right, it is evident that the sound will reach my right ear taking less time than it takes to reach my left ear. Our auditory system is capable, in optimal conditions, of grasping ITD of the order of 0,1 millionths of a second. Furthermore, the ear furthest from the sound source will be in a sort of "shadow zone" formed by the obstacle of our head and will therefore receive the sound with a lower intensity than it is received from the other ear. This difference in intensity is called IID (acronym of English Interaural Iintensity Difference).
By processing the IID, the auditory system receives further information on the direction of the sound's origin. The first of these two “strategies” (arrival time) is very effective for low frequency waves (and wide wavelength) for which the obstacle represented by the listener's head is easily bypassed.
The second strategy (sound intensity) is very effective for high frequency (and small wavelength) waves for which the obstacle represented by the listener's head is very important and determines a significant decrease in sound energy. However, these mechanisms are not able to resolve the front-to-back ambiguity, and to discriminate the elevation of sound (high-low), operations for which our auditory system uses the "filtering" that the head and the auricles operate on incoming signals. This is the "transfer function of our head" (Head Related Ttransfer Function: HRT extension), i.e. the way in which our head and auricles modify the sounds that reach the eardrums. These changes are given above all by the physical conformation of our head and of the auricles that modify the incoming sound, varying its content in frequency and phase. One of the first techniques used to make one binaural registration it was the most intuitive one, that is to make one mannequin head, built in such a way as to reproduce the sound absorption of a real human head and its function as a natural separator between the right and left ear, equipping it with auricles and positioning two microphones inside the ear canals. In this way the microphones pick up the sound that is modified in a similar way to how it is modified by the shape of the human head, in the way most similar to how it would be perceived by a real listener.
One example is the beautiful professional stereo / binaural microphone head Neumann KU 100.
In the digital age, DAWs and audio plug-ins could certainly not be missing with and tools to make a binaural mixing. An example is plug-in AMBEO Orbit of Sennheiser, which allows us to position any sound (a musical instrument, a sound effect, a voice, etc.) in the three-dimensional space and thus create a richer and more enveloping mix, bringing us closer to the perception of the sounds of real life ( with sounds coming from different spatial directions). The AMBEO Orbit plug-in is Free and available in AAX, VST, VST3 and AU formats for both Mac and Windows.
It is very simple and intuitive in its operation, let's see its main features to move on to its concrete use in a mix session.
The plug-in has the following parameters for controlling and positioning the sound:
Azimuth
This parameter controls the horizontal position of the sound and is expressed in degrees: 0° corresponds to perfectly front positioning (Front), 90° right positioning (Full Right) e -90 ° perfectly left (Full Left). TO 180° the sound is placed perfectly behind, behind the listener.
Elevation
This parameter determines the vertical position of the sound, and is also expressed in degrees: 0 ° corresponds to the level of the listener's ears, 90 ° corresponds to the maximum height, and -90 ° to the lowest value (in height) of the sound positioning.
Width
When the plug-in is inserted on a stereo track this parameter controls the width (distance) between the left and right channels. Setting it to 0 ° the track becomes monophonic. If the plug-in is applied to a monophonic track, the parameter is disabled.
Clarity
The HRTF filters used by the program alter the frequency response and the timbre of the sound, especially if you make "extreme" positioning. Generally this is not a problem but if we notice some anomaly and want to restore the sound to its original character we can use this parameter (naturally losing part or all of the spatial information, depending on the Clarity value set).
Reflections
With this parameter we can add acoustic reflections to the sound that we have placed in the three-dimensional space, with the possibility of deciding its intensity, as well as the size of the room and the material of the walls.
A "binaural" mixing, ie in which the sounds are positioned in three-dimensional space using those mechanisms such as the HRTF filtering that are typical of human auditory system, in its workflow is very similar to the classic stereophonic mixing, but some clarifications are needed in this regard. As far as the listening system is concerned, mixing via monitor audio is not recommended as much of the effect of the three-dimensional spatialization.
Instead, a mixing with headphones and then a re-listening with the speakers to make some small adjustments to the mix. This is because some sounds that are present when listening with headphones may tend to disappear when listened to with monitors, hence the need for a fair compromise between the two to make the sound enjoyable in both situations. Also the so-called are recommended open headphones (open-backed headphones) instead of the more common closed-backed headphones, I personally use the AKG K612 PRO, open over-ear reference headphones able to offer a natural sound image suitable for professional monitoring.
Moving on to the work session in our DAW (in this case a system Protools) and looking at the following image we notice how the AMBEO orbit is found in "insert" on all the channels of the sounds that we want to place in three-dimensional space, and is positioned as the last of the plug-ins that are in the insert chain .
Some tracks of the session were initially monophonic but the Orbit automatically converts them to stereo when placed on a channel. As we would do with a simple stereo pan we can now decide to place the sounds in a precise static position, or to automate the plug-in parameters to create a movement. For example, we can position the barking of a dog behind us, the song of a bird frontally and to the right (and elevated with respect to the listening position), and at the same time automate the Azimuth parameter to hear the sound of a person's footsteps. that walking starts from the front position to move to the left and then move away behind us.
Some of these placements in three-dimensional space can be considered as small details that are not too significant (and this is also true in the multichannel mix), details of which the viewer is barely aware (if not totally unaware), but in reality they contribute to the richness of the scene and immersion by the spectator in the world represented by the work as a whole. In fact, let's not forget that the viewer's attention is a process in which innumerable factors intervene, referring now in particular to the audiovisual work we have first of all the dramaturgy of the narration, the visual aspects, the charisma of the characters, the music and so on.
However, the richness and quality of the sound system act in a profound and subtle way and constitute a very important contribution. We also have the possibility of creating real special sound effects with a much more vigorous impact, for example, imagine a meteorite passing to our left with a powerful sound that touches us from the front and then moves away behind us. Overall the sound performance and the overall result in the use of this technology, as far as my experience is concerned, was excellent, with only one negative note: the impossibility of having a control that allows you to go from front to back without being forced (as in the Azimuth parameter) to move completely left or right. In this way we could automate (also using the Elevation parameter) more realistic movements directly above our head such as airplanes, helicopters, etc ...
There is also the possibility, as with other 3D audio plug-ins, to choose between different Output formats, such as Ambisonics or traditional multichannel formats. However, it is a technology intended for a small number of applications (for example to create binaural music or to be implemented in some Games and in virtual reality where headsets with integrated audio headsets are used.)
As we have already said, binaural audio is in fact usable only through stereo headphones, as opposed to formats Multi-channel 3D in which loudspeakers are used. For the latter (such as Dolby Atmos or DTS: X) sound bars are even available consisting of a single component (within which multiple speakers are housed) capable of reproducing the countless channels of which these formats are composed. An example of this is the soundbar produced by Sennheiser and which, like the Orbit plug-in, is also part of the AMBEO series of products dedicated to “immersive” audio.
Le soundbar use the reflections on the walls room to play the surround channels, both rear and ceiling channels, as you can see in the following figure. In this way you can avoid having a large number of speakers inside your living room and home, as well as mounting brackets and speakers on the ceiling, but certainly the overall yield is not comparable to that of a complete system.
To conclude, we are faced with a very large and extremely complex field, and this is just a starting point, we will have the opportunity in the future to deepen this and other topics of the fascinating world of “immersive”, multi-channel and three-dimensional audio.
(Ps: We leave you with a demonstration video, which we mixed using the plug-in, and which more than words demonstrates the potential of this technology. Remember to listen to it with headphones.)
USEFUL INFORMATION
Link: WIDE ORBIT
