Perception and cognition
The role of the brain in perception is particularly important because it provides a large work of analysis to distinguish, recognize and evaluate the sounds, according to their height of course, but especially according to their evolution during time (the term emotion drift étymologiquement of this direction of the movement). The brain allows also the correlation between the two ears in order to locate the sound in space (difference of intensity and phase). It is also him which enables us to recognize a musical instrument or a precise person. The ear, it, does nothing but transmit rough information. It would seem, but the always virulent debate is open, that most of the work carried out by the brain is learned and noninnate.
Thus, the perception of the stamp, and even of the Justesse can vary from a person with another, independently of its personal tastes, not only because of degradation of its auditive system, but also because of a deterioration of its neurological faculties. Another reason of this difference in perception is due obviously to the filtering carried out by a growing old auditive system. Thus, just as an optical filter masks or highlights elements of an image, the ear can mask or highlight the components of the sound, varying from as much its perception.
The psychoacoustics is the study of the auditive feelings of the man. It is thus located at the border between the Acoustique, the physiology and psychology. acoustics will study the nature and the properties of the sound Onde S which arrive at the tympanum. The psychoacoustics will study how they are collected by the auditive system and the way in which they are interpreted by the Cerveau. From this study one deduces that the perception of the characteristics of a sound does not have objective values of measurement. The attributes of the sound are the result of a mechanism of decision at the neurophysiological level.
Perception and feeling
The perceived phenomena cannot be measured on a scale of continuous measurement. It is above all the temporal phenomena, i.e. their measurement is not constant for every moment (T) of the vibration. To render comprehensible to us the sound phenomenon such as it falls under time, the Sonagraphe, apparatus appeared in the years 1950, used a three-dimensional representation (frequency, Amplitude, time) which, though convenient, remains coarse. Psychoacoustics must thus contribute to the study of the relations between acoustic parameters and significant attributes.
The human Oreille is a complex, imperfect body but however very powerful. Some affirm that the two directions of the Art are the Vue and the Ouïe (that disregarded curiously the Goût that nature and certain cooks also raised with the row of art, just as the Toucher and the Odorat are artistic field: perfumery, textile, sensual, the debate is here to recognize the psycho-cognitive scale of art in itself), because the sensual operative fields extend from the immediacy to the depths of the unconscious one. The sight made it possible to collect objects, therefore to name them and to draw some from the concepts. It is at the base of the scientific reasoning. The vocal apparatus, which gives to (D) hearing sounds organized in language, can as for him transcribe these concepts only in one transitory form. This transitory is at the base of the load of emotion which the music transports. Hearing, by collecting these transcriptions, thus collects more the emotion that concept, because it cannot fix them. Information is there consequently more order qualitative than quantitative, and the ambiguity of the measurement of this information is included/understood better. hearing and the sight are both direction which transmits information to us over time and space. But the inequality between the sound radiations and the light radiations is for much at the origin of an obvious inequality between these two directions. The threshold of feeling of a sound by the ear is located at W, when the threshold of feeling of a specific source of light (with the naked eye) is located at W. the Vue is thus a direction reserved for the immediate one. Hearing, by conveying indications of another kind, informs us much more on what is field of the emotion, feelings: for example, in addition to it can carry more information, the voice on the telephone can say of it to us as much on the psychological state of the interlocutor that a photograph.
Auditive illusions
The psychoacoustics, helped in that by the tools of the sound Synthesis, cleared up certain particular phenomena of interpretation: auditive illusions. These illusions were particularly studied by John Chowning (pioneer of the numerical synthesis of the sounds) then by Jean-Claude Risset, researchers and type-setters, who, using the computer created several forms of illusions integrated in their works. The form more envoûtante of illusion that which makes it possible to recreate phenomena against nature, otherwise is called paradoxes. In these illusions, our cognitive diagrams are opposed to incongruous associations. Jean-Claude Risset, who studied their mechanisms in the auditive field, came from to compose several by means of the computer of them. He published on the matter of many articles which clarify all the difficulties of apprehension of this problem. Let us try to summarize the matter here: In German, the vocabulary recognizes for the same concept of “its”, two concepts, Your and Schall , which distinguishes two components heights that French, does not distinguish to him: the tonal height ( " " ), related to the variations frequency, and spectral height ( " " ), bound, it, with the position of the center of gravity of the components of the spectrum. This spectral height characterizes the brightness of an instrument. If, as can do it the synthesis of the sounds by computer, one succeeds in separating the variation the tonal height (by displacement of fundamental) and that the spectral height (by modification of the spectral envelope), one can succeed in creating variations paradoxical heights. For example:
- - sounds giving the impression to go up or go down without end (fixed tonal height). These experiments were taken again generalization of work of Roger NR. Shepard on the circular chromatic range and are usually represented visually by the staircase of Penrose. Mutations of Jean-Claude Risset is a work where the harmony is unceasingly prolonged in the stamp, and which gives to understand this paradox.
- - sounds going down while becoming acuter (tonal and spectral height varying in opposite direction), transposition in the sound field of the visual effect carried out by M.C. Escher in its Cascade .
Influence age on the hearing impairment
This figure shows the influence of the age on the hearing impairment at various frequencies. According to the quoted sources, the results are different. That is easily explained by the fact why great variations are observed in the population and that these studies have evil to take into account only the age of the individuals. It is not rare to see old musicians with ears of young man, just like there exist young people with ears prematurely degraded by exposures repeated to too strong sounds such as those of the Concert S or discotheques.
Classically the age involves a presbyacusia which appears by a hearing impairment on the acute ones. There exists also a reduction in the cut-off frequency on the acute ones. The acute cut-off frequency is the frequency beyond which a person does not perceive anything any more, whatever the volume used, i.e. limit, for this person between sounds and ultrasounds. Certain work showed that there also exists, in a way more difficult to include/understand from the physiological point of view, an increase in the cut-off frequency on the low registers. I.e. the limit between sounds and let us infrasons lets gain the latter.
Hearing impairments due to the noise
The hearing impairments due to the Bruit depend at the same time on the exposure time and the intensity of the noise. Notice that one indicates here all the sounds like “noise” and not only those which are unpleasant. Thus, to listen to music with the helmet with full volume or to look at the planes taking off of the airport has exactly the same effect on the auditive cells. It is appropriate can be to moderate this observation. The P Pierre Josserand, trying to quantify it made pass an audiogram to Instrumentiste S of Hard rock before and after their repetition. It had posed the assumption that, considering the Amplitude S used (using Amplificateur S important), the audiogram post-repetition would be deteriorated, Statistique lies speaking, compared to the audiogram handle-repetition. The Hypothèse die departure could not be confirmed. It was verifiable only on some exceptional individuals but not on the whole of the Population. Josserand interpreted this result like the indication of a protective effect of the Attention of the musicians and owing to the fact that before any excessive sound, their ear was " préparée" because it is themselves which were at the origin of this sound.
Note that the effects of a Bruit excessive and/or impulsive are different from those of the age. With the age, the ear becomes less sensitive to the high frequencies whereas noise exposure decreases especially the sensitivity around 3-4 Khz, frequency where the just ear is most sensitive. A " then is observed; encoche" or " auditive Scotome " on the 4000 Hz of the Audiogram. This type of hearing impairment very frequently meets in the users of firearms, because it is characteristic of the people exposed to the strong sounds and percussifs. Especially during an insufficient use of adequate auditive protections (ear-protection headset)…
Amplitude as in Fréquence. More the audible high frequency by the human ear is thousand times higher than lowest and the sound most extremely can be an audible billion times stronger than weakest (a report/ratio of intensity of 1012 with 1).
Thus, calculation shows that a doubling of the intensity accounts for 3 dB. For the ear of certain subjects, this variation is perceptible but one needs an increase of 9 dB of the acoustic intensity so that the human being has the impression of a doubling of the force of the sound. That represents in fact an acoustic pressure 8 times stronger! In audiometry ORL, one considers that a variation of less than 5 decibels should not be taken into account. Sights the conditions of catch of measurements, one takes really account of a difference in thresholds only starting from 10 decibels.
In frequency, it is the change of octave which corresponds to a doubling of frequency. There too we thus perceive linearly the evolution logarithmic curve of a phenomenon Physique. -->
Virtual reality and psychoacoustics
The studies relating to psychoacoustics influence much the techniques of restitution of sound scenes virtual. The listener is surrounded by a sound environment often associated with a visual environment.
The stereo, appeared in the mileu of the years 1950, is the first acoustic example of virtual reality. One plays simply on the balance between the level of emission of a loudspeaker located on the right of the listener and a second located on the left. One thus gives the impression which the source of sound moves from right to left or conversely. System 5.1 is only the continuation and the improvement of stereophony.
Since, the expert learned how to play on the phase of the wave coming from the loudspeakers. He also learned how to include/understand the phenomena of diffraction of the sound wave around the face of the listener, phenomena who allow the man to locate the sound source without seeing it (one is able to locate an alarm clock who sounds without seeing it). The knowledge of these phenomena with license to conceive systems known as binaural (of the binaural singular).
In parallel, one tries to invent systems of restitution based on the properties physique of the sound field. One finds in these categories the Holophonie and the Ambisonie. The holophonie rests on same the principles as the visual holograms whereas the ambisonie prohibits any other treatment that a simple filtering of the signals. A particular form of holophonie baptized " 3D phonie" by its inventor (corner audiophilehttp: /www.apiguide.net/04actu/04musik/coin_audiophile.htm) utilizes an additional stereo vertical way placed in withdrawal compared to the stereo frontal ways. This technique, founded on the effect of chorus, very old and well-known phenomenon in classical music, avoids any filtering of the signal. Without reaching real matérialisation 3D of the sounds in space, it makes it possible to confer on the virtual sound scene a very convincing life.
See too
- Absolute pitch, relative Ear
- Hearing
- Hearing
- Its (physics)
- Acoustics musical
- Psychophysical
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