SCIENCE DISCLOSES SURPRISING NEW ASPECTS ABOUT OUR
ABILITY TO HEAR.

Introduction

Why have audio systems of good quality that present only small measurable differences in the electro-electronic parameters been evaluated by the greater public and yet received so many different assessments? Why has the same audio system been judged with such different opinions, some even antagonistic? Why does the quarrel around the correct sound produce such excitement and heated debates? What factors do we take into consideration when evaluating if a sound is pleasant or not? Do we judge a sound by what we are accustomed to hearing?
       According to international research, there have been impressive advances not only in equipment and systems for sound evaluation, but also in understanding how the human being perceives sound. These two fields of science, even though very distinct, are intimately correlated as we will see in this article and in the articles that follow.
       Reading some international magazines on this subject, I have assembled interesting information and insights that I intend to present in this article. We will talk a little bit about this new knowledge, expecting to contribute with our Brazilian market, immobilized by its economic situation, and each time more restricted to a smaller number of audiophiles and music lovers.
       Let’s begin with history from way back. In 1863, a book called "the Sensations created by the Tones as a Psychological Base for the Musical Theory" of Herman Ludwig Ferdinand Von Helmholtz (1821 the 1894) was published. Helmholtz was a physicist and a mathematician, born in Potsdam, Germany. He presented in his book a study on the differences of the human perception of sounds and musical tones. Through this study, the author raised the hypothesis of the probable existence of two distinct groups of listeners: synthetic and the analytical ones.
       At that time, these findings of Helmholtz did not raise much fuss, due to some of the acoustic devices that were presented in his same work, such as the famous absorber that takes his name today, which was considered a great novelty at that time. But since the 20^th century, some universities have deepened the studies on the human perception of sounds, initiated by Helmholtz.
       In the depths of the Department of Neurology of the University of Heidelberg, Germany, Dr. Peter Schneider, of the Section of Bio-magnetism, with scientists of the Universities of Liverpool and Southampton, in England, through diverse auditory and physical medical experiments, managed to show that human beings listen in different ways to the same sounds and tones. Today it is a scientific fact that each individual perception of sounds and tones are extremely differentiated.
       This new knowledge is leading to a revision of the concepts of sonorous electronic equipment evaluation that we will talk about at another opportunity.
 

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Synthetic and the Analytical Listeners

The research of Dr. Peter Schneider confirmed the suspicion of the German scientist Herman Von Helmholtz,  who, more than a century ago, said that there are two distinct groups of people regarding auditory perception. He divided them as the listeners of fundamentals and the listeners of the harmonic tones. In this article, to simplify, we will call these two groups as Helmholtz originally defined them in his famous book. The group of the synthetic listeners synthesize the sound around its fundamental and the group of the analytical listeners base their perception on the harmonics of the sound.
       As the research had shown, none of these two large groups hears better or worse than the other one. It was found that the way one hears does not depend on sex, race, profession, age or individuality. The research established that these two groups simply hear in a different way one from the other, as we will see further on.
       The sound is formed by one fundamental and its harmonics, where the harmonics are sine waves in multiple frequencies of the fundamental sine wave.

       This graph is a representation of a complex sound or complex waveform. A complex sound is the sum of different sine waves. Any non-sinusoidal waveforms, such as square waves or even the irregular sound waves made by human speech, can be represented as a collection of sinusoidal waves of different amplitudes and frequencies blended together. The technique of transforming a complex waveform into its sinusoidal components is called Fourier analysis.  Each column of the graph represents one of the sine waves of the complex sound, each column, with two informations: the frequency and, or the volume, or the sound intensity, or the voltage, or the power, in percentage. The first column is called the fundamental of the sound and is very important to define the pitch of the sound and all others sine waves are the harmonics, which form, with there volumes and frequencies the timbre of all different instruments, or human speech, or other sounds. For example, the C4 note of a piano is a complex wave were the fundamental is at 261Hz and there are multiples  in higher frequecies, which define the timbre of the piano. Each of us hear these complex sounds in a different manner, according to the kind of listeners that we are: synthetics or analyticals.

The group of the synthetics guide themselves based on the fundamental frequencies of the sound, while the analyticals guide themselves based on the harmonics of the sound.
       Not too long ago, before these new findings, it was assumed that when a sound was emitted without its fundamental tone (for example, the reproduction of a bass sound in a speaker), the human ear would have the capacity to reconstitute, this fundamental missing, and thus, to listen to the entire specter of the sound. However, new tests have demonstrated that only the synthetic listeners have the capability to reconstitute the fundamental tone of a sound. The analytical ones, as they base their hearing on the harmonic tones, do not reconstitute the fundamental tone.
       Each individual is classified as an analytical or synthetic listener according to a specific scale design for this purpose. For the synthetics, the scale goes from 0 to -1. The "synthetics  -1" are the ones that are mostly oriented by the fundamental. For the analyticals, the scale goes from 0 to +1, being that the "analytical +1" are the ones that are mostly oriented by the harmonics of superior order. Therefore, synthetics and analyticals meet only in the point 0 on the scale. It is important to emphasize that each person can be classified at one point of the scale from -1 to +1. In my case, for example, I am synthetic -0,2. The people, in different positions in the scale, not necessarily hear better or worse, but simply each one hears in a specific, different way. The musical perception can be very differentiated. For example, there are people who can hear the same sound up to four octaves higher than the others!
       The graph below presents the distribution of the people, in the -1 to +1 scale, according to research done by the University of Heidelberg. Curiously, it indicates that the majority of the people are found in the extremities of the scale. That means that a big part of the synthetic listeners are between -1 and -0,5 and a great part of the analytical ones are between +0,5 and +1. These findings can partially explain why we differ so much in the way we perceive the sound of music, since most people are in the extremities of the scale.

These facts have been triggering new studies with very interesting discoveries specially in relation to the evaluation of audio equipment in the international media. Initially, the Reviewers of Critical Listening (RCL) that judge the quality of the equipment for specialized foreign magazines have been submitted to tests. It was disclosed that the best reviewers are the ones that are the synthetic and analytical people found closer to the center. This finding made the audio international media realize the need to carry-out auditory tests on RCL candidates. And from the results of those tests, the magazines are now choosing which are the more appropriate people to be the RCL, and so, part of the publishing body of the magazine.
       But the discoveries do not stop here! The University of Heidelberg, carried out examinations of nuclear espintomography of the human brain to show the anatomy of the right and left cortex where the musical perception occurs. Also magnetoencefalography examinations had been carried out to determine electric currents in the right and left cortex of the brain. The results are surprising! They show that the gray matter of the left cortex (in the region responsible for hearing) in the synthetic listeners is bigger than the gray matter of the right side. On the other hand, the analytical listeners have the right side more developed. The electric current is also greater on the left side in the synthetics, while, in the analyticals, it is greater on the right side. Professional musicians are also classified as synthetic or analytical listeners. Even though they have more cerebral mass in the hearing region of the brain than non-musicians, the proportions also differ depending on what type of listeners they are, synthetic or analytical.
       The cortex of the left side, more developed in the synthetic listeners, is very sensible to fast impulses of sound, mainly those that do not exceed 50ms (milliseconds) of duration. Rhythmic sounds are a preference of the synthetic listeners, while longer pulses are a preference of the analytical ones, whose right cortex is more developed as we have seen. Therefore, longer sounds that are more melodic are better perceived by the analyticals. We can not forget that the pitch of the frequency of the perceived sound can vary, being around the fundamentals for synthetics, and for the analytical ones being able to go up to four octaves higher than the fundamental of the same sound.
       These differences are evident and they also explain the distinct preferences for musical instruments between the two distinct groups. While the synthetic listeners prefer the instruments of percussion, guitar, piano, and brass instruments such as trumpets and transversal flutes, the analytical ones prefer the string instruments such as the violas, the bass, and brass instruments and singing. Differences between the analytical and the synthetic listeners have been perceived even in the way they play instruments. While the synthetic ones value the rhythm of music, the analytical ones value the musical melody.
       It is interesting to notice that because there is a division of preferences for different instruments between the two groups, we can also identify if they are analytic or synthetic by the localization of the instruments inside of a modern orchestra. Thus, those of the left side of the orchestra are normally the instruments preferred by the synthetic listeners, as for example, the instruments of percussion, the piano, and the high violins. It is curious, and the research has also shown that the majority of the teachers belong to the group of the synthetic listeners. On the right side of the orchestra, the side of the analytical listeners, are instruments such as the bass violin, the viola, violoncelo, the double bass, tuba, saxofone, the flute, the bassoon, oboé, and also the choral. Therefore, as we can imagine, the main differences are in the band of frequencies that go until 1.500Hz. (the bass goes until 160Hz and the midband until 1.300Hz).
       And the discoveries don't stop here. There is more!
       Another study was carried out to understand the preference for brands of equipment of electronic reproduction of music, such as speakers, record players, CD-Players, integrated amplifiers, receivers, and amplifiers, between the two groups. This study revealed astonishing results. It is almost incredible, but there is a correlation between brands and types of audio equipment and the punctuation given by synthetic and analytical listeners. Thus, for example, a speaker of a certain brand is preferred more than other speakers by the synthetic listeners that have a punctuation on the scale of around -0.5. Going further in the investigation, one found out that the designers of that same speaker, of that specific brand also belong to the same group, or in other words, to the synthetic -0.5 listeners. Another example documented that one integrated amplifier of a certain brand was preferred by analytical  listeners of +0.7. Further, it was verified that that equipment  was projected by people also pertaining to the same group of listeners as the consumers (+0.7). There are, therefore, different brands of devices for the two groups of listeners, synthetics and analyticals and all ranges.
       These discoveries will bring great changes in the marketing and the design of audio equipment to such an extent that we are not able to visualize it today.

Conclusion

We have presented the most recent discoveries in the field of the human musical perception. There are basically two types of listeners: the synthetic and analytical ones. They are two distinct groups that hear simply in a different way, independent of the age, sex, color, etc. The group of the synthetics guide themselves based on the fundamental frequencies of the sound, while the analyticals guide themselves based on the harmonics of the sound. We have shown that according to statistical surveys, the majority of the synthetic ones and the analytical ones are in the extremities of a scale, and the reasons for this are still unknown. We have shown that there is evidence of a correlation between the instruments chosen by the musicians and the group they belong to as listeners. Also, it was interesting to notice that the division of the cerebral cortex, in analytical and the synthetic listeners, corresponds with the division and rank of the instruments in a modern orchestra.
       We now have in front of us new concepts of hearing that let us foresee significant changes that are to come in the near future. With certainty, they will influence the design of the equipment and also the marketing of the companies of audio. On the other hand, the research has not stopped here, it continues intensely. It is probable that our personal musical trends are already pre-programmed genetically and studies in this direction are on the way.
       Today we can go through tests and verify if we are synthetic or analytical listener. Knowing this, we are able to indicate which brands and equipment of audio  corresponds to the preference of each individual, or even, which ones we will find most pleasant. This, without a doubt, has simplified the choices, and the purchase of the equipment will become more objective. The assembly of an  audio system with this process is made easy.
       I ask, " What type of listener are you?"
 

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