Illustration: Roman Alsina
Illustration: Roman Alsina

In search of the lost "D": immersive sound

9 minutos / Alfonso Peña

03.04.2020 / Articles

(We recommend using headphones when reading this text for a more complete experience)

In the late 1980s, I can't remember exactly the year, I was working in Italy when I met Alfonso Belfiore, a music genius, professor of Art and Technology at the Florence Conservatory. Because of our similar tastes, we became friends and he invited me to listen to his most recent work in his studio, located in an old mill in the Tuscan countryside. It was a serie of records that compiled the work of choirs from different regions of Italy, all recorded live in cathedrals and churches.

I settled in front of the speakers of an excellent Hi-Fi system, and prepared to listen to the album chosen by my host: Lacio choral singing. As soon as the first track was playing I thought: what a strange sound, without depth, confusing, what a bungling! Alfonso, with a mischievous smile that betrayed the expectation of my evident reaction of displeasure, asked me: ah, you don't like it, do you? Without waiting for an answer, he gave me headphones. When I did, my face lit up and my eyes popped out of their sockets in surprise. Suddenly I was transported to a Roman church, where a large choir, accompanied by a majestic organ, surrounded me playing a liturgical song. He was for the first time in the presence of a holophonic recording, obtained using the binaural method.

Over the past few years, surround sound, immersive, or whichever D you want to rate, has gained popularity among music lovers and audiophiles. Perhaps 3D does not do justice, but 8D?!; Don't you think it's too much?

There is not as much new in it as many think. Undoubtedly, its current popularity is basically dictated by the preference of listening to music through headphones, linked to the proliferation of portable audio players (iPods, mp3 players, cell phones) and video game consoles. Listening to phonograms obtained through the binaural method requires the use of headphones, not being attractive through speaker systems, however their efficiency and fidelity.

The binaural phenomenon, from which this method takes its name, consists in the ability to perceive sound signals through two ears located on either side of the head, and to be processed and interpreted by the brain, which determines the direction of arrival of the different sounds, the distance and the specific space in which the sound sources that emit them are found. This does not mean that with one ear we are not able to discern where the sound comes from, because in this process the shape and dimensions of the head play, and the work of the brain, capable of creating a judgment from the accumulated perceptual experience.

A sound stimulus from one side reaches one ear with certain interaural differences from the other. In other words, the binaural effect is basically conditioned by three main factors:

Time: due to the distance between them, the sound wave affects first the ear nearest and in a certain time interval later on the opposite one.

Intensity: upon reaching the opposite ear the sound wave loses amplitude, after traveling a greater distance and finding itself at the head as an obstacle.

Color: due to the screen effect that the head exerts due to its shape and dimensions, the sound wave diffracts and, consequently, it undergoes alterations in its spectral content (color).

These factors are evaluated by the brain to establish the location of the perceived sound. To this are added the reflections that occur on the existing surfaces in the room where the sound was emitted. These behave like secondary sound waves, and equally reach each other with different intensity, arrival time and color, thus enriching the information provided. With all these elements, the brain is able to create a well-defined image of "where did that sound?".

Sound recording using the binaural method is based on this same principle. For this, an “artificial head” is used (although there are other binaural microphone designs), manufactured with dimensions, shape and texture similar to the human head, with two microphones with an omnidirectional directivity pattern located in the corresponding left and right ear canals. This device captures sound in the same way that humans do. For this reason, the stereo phonogram obtained with these devices, although compatible with reproduction in loudspeakers, achieves greater realism, a sense of space and depth if it is listened to through headphones.

In case I had not been convinced with the “holophonic choir”, Alfonso Belfiore reserved for me as a dessert a unique recording that he made hanging the artificial head of a traffic light located at a four-way intersection with heavy traffic. The effect obtained was amazing. The virtual image transmitted with great veracity the movement of the vehicles in all directions around the head.

A similar experience of more recent invoice is Virtual Barber Shop, produced in 1996 by QsoundLabs, and affordable on online platforms. It consists of an audio clip obtained using the binaural method, in which the listener takes the place of a barber client who, during her haircut, experiences with incredible realism all the surrounding sounds. It is noteworthy that, unless you listen with your eyes closed, the virtual sounds supposedly coming from the front do not manage to occupy that position fully. The brain is not easily fooled if it visually perceives an image that does not correspond to the auditory stimulus. However, as soon as we close our eyes, the virtual front sound becomes more accurate. We fool the brain!

I tried to keep the sequence recorded from the traffic light on the support I had at that time, an audio cassette (CDRs or other digital media were not yet available to everyone). The result was not the most reliable, since the magnetic tape was not able to cover the entire range of high frequencies, largely responsible for providing the virtual source with valuable information about its spatial location. Today, thanks to the wide spectral tuning fork that digital audio provides, this deficiency has been overcome. That's why I think that the lack of adequate support and the then unusual use of headphones made holophonic sound not popular for years

It was not until 2012 that multidimensional sound rose a new rung. With the premiere of the Brave tape in movie theaters equipped with 9.1 Dolby Atmos technology, the viewer was able to enjoy spherical surround sound. Unlike all these sound systems, in that each virtual source starts from its own discrete emitter (what sounds behind, to the right, arises from a loudspeaker located in that position, or from two or more loudspeakers if it occupies an intermediate position between they), the binaural sound is still stereophony, although it is more realistic thanks to the greater use of psychoacoustic phenomena.

No fue hasta 2012 que el sonido multidimensional ascendió un nuevo peldaño. Con el estreno de la cinta Brave en salas de cine equipadas con tecnología 9.1 Dolby Atmos, el espectador pudo disfrutar de un sonido envolvente esférico. A diferencia de todos estos sistemas sonoros, en que cada fuente virtual parte de su propio emisor discreto (lo que suena detrás, a la derecha, surge de un altavoz situado en esa posición, o de dos o más altavoces si ocupa una posición intermedia entre ellos), el sonido binaural no deja de ser estereofonía, aunque es más realista gracias al mayor aprovechamiento de los fenómenos psicoacústicos.

Currently, in addition to the use of binaural recording methods, some software developers have introduced applications that allow obtaining holophonic phonograms using existing recordings as raw material. These are based on the use of algorithms obtained from the analysis of the relationship between the physical parameters of the incident sound and our brain's interpretation of it. They have a graphic interface that allows the object to be positioned or displaced, transcribing to the program the movements that the sound source is intended to make, and correspondingly the algorithm enriches or modifies the processed audio signal with artifacts that deceive the brain, making it believe that the Sound comes from one or the other direction.

At the dawn of stereophony, many artists used it solely as a novel, albeit artificial, and implausible effect, placing, for example: the voice on one speaker and the band on the other, or shifting the trumpet from one end to the other for no reason any. This sparked interest for a very short time, as the prevailing concept was to use the new tool in a more creative and realistic way.

Today history repeats itself. It has become fashionable to use the binaural technique as a simple gimmick, which has managed to attract the attention of many listeners, dazzled by the "novelty". In a few years, who will want to hear Céline Dion circling our head like a satellite as she sings My heart will go on? However, many other creators have embraced this technique as a useful and indispensable tool to take their works to a new sound dimension.

Assuming that the artistic criteria prevail over simple effect, holophony can open new horizons in the sound universe. Immersive sound shows that accommodate the listener in the concert hall, virtual reality video games with surround sound where the characters move in multidimensional spaces, telefilms with binaural audio between their tracks to choose, audio clips intended to relax or help reconcile sleep are just some of the great benefits that this new concept of sound can bring us ... from the last century.

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Alfonso Peña

Cuban sound engineer with more than 30 years of experience in the Cuban music industry. Your texts and some examples of your professional contributions can be found on his blog https://piprofessionalaudio.home.blog/

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