La psico-acústica

Psycological and mental occurrencees during hearing process

Hearing occurs in your head. After sensory perception by the ear, sound is subjected in the internal ear and the brain to many compression and calculation procedures. The three qualitative attributes sound characteristics, source position and acoustic:specifics of a room.

1. Sound Characteristics

The sound properties of a sound incident, i. e. the frequency spectrum and the loudness level of particular frequency ranges give information about the source of sound. In this regard, the human hearing develops the subtlest differentiation in range of the human voice and idiomatic meanings, which may range beyond any available measurement precisions. So a person may not only be recognised by voice, but also by mental and physical conditions, which are subliminaly perceived.

This disposition affects our musical sensation, our sound preference, which hold universally validity over all individual aspects. Thus stringed instruments, the violine in particular, take an exceptional position beeing most alike the frequency character of the human voice. “God” or “bad” Instruments differ emotionally from another by sound like “fit” or “unsound” fellow men. The luthier optimised his mechanical skills in this regard and the virtuoso intuitionally takes advantage of this compound of voice and mental disposition to illustrate moods by specific overtone selection.

2. Acoustic Source Position

The position of a sound incidence is stereo acoustically analysed by means of interaural time differences, interaural level differences as well as specific frequency spectra at the right and the left ear. At this auricle as well as the cochlea affect the quality of each parameter in a caracteristical manner rendering more precisely the information content of the perception by factual spreading.

The human aural sense achieves an astonishing high resolution in processing all the different parameters synchronously as well. A sound source within the reaching area of the hands may be localised on the point. Elemental alterations of position, direction or movement are sensed.

Differences in time and sound intensity are accountable for horizontal localisation in binaural hearing. Overtone patterns open up the vertical dimension and the spectral right/left difference again expands the horizontal and completes the three-dimensional perception by focusing effects.

An other deternining factor of spatial localisation, that plays a prominent role in the multimedia subject Virtual Reality, is the relative position resp. movement of the head in regard of a sound source. The heads position or turnaround of the head are grasped by the sense of balance and rotational movement of the innner ear as well as by sensory receptors of position in skeletal joints and further aggregated with the hearing information to a higher level of perception. As a result of he high extended sensory precision the eyes on their part will focus while turning towards the source of sound.

3. Acoustical Response: Specifics

The human acouesthesia is able to locate multiple acoustic sources (even moving ones) and to process them apart. The selectivity in that is respectable. Alike sensory processing in the eye this is reached by physiological and “computed” masking or amplification at the adjacent sound incidence. At the same time the number of incidences to be processed is quasi unlimited (assured researches regarding this are missing yet). This is attained by selective priorisation of qualitative changes under processing modes similar to Thread programming or Time-Sharing in computer technology.

The Perception of the surrounding space arises in just the same manner. Each echo, each reflection will be thereby a different acoustical incident. Every room represents so its very own trait with specific profile for every point in that room. In this way it is a question of very complex acoustic cumulative formations with involved correlations. The listener processes this spatial impression according to the specified run and comes up to sensation of heraring by the sum of his individual experiences.

At least the acoustic properties of a room comply with simple rules: the acoustic will be regarded as “well” if it supports the mentioned sensoric processes, if it effectively spares effort the sense of hearing. In this good separation property is important as well as a well-balanced resonance. Basically the direct sound incidence has to dominate the room acoustics. Acoustical swash effects must be prevented and in particular the reverberation has to show a homogenous progress. In this regard tall cathedral halls for instance are problematic in particular in cold seasons because of thermoclines or thermal striae above heating outlets. The trained ear may of course be bothered by this.

Aspects of authentic sound and acoustic reproduktion

1. Experience-based auditory imprinting

Individual and subjective acoustical perception is an interaction of physiological components, as described, and acquired multisensorial individual experience, accumulated in life.

As much as vision the auditory perception has just to be learned in infant development. Both orientation senses will develop directly interdependent. Just a mental connection of unicausal visual and auditory incidences will allow orientation in space. Later the experience will suffice, to complete an incidence mentaly associativly: I will for instance identify and localize a musical instrument without having to see it, or I will anticipate the drumbeat while seeing the drumstick coming down.

It is easy to understand, that these experiences just will reference the natural configuration of the sense organs. A sound event that is e.g. recorded with widely spaced stereo microphones will not longer be in line with personal auditory experience, it just causes vague perception patterns. In the same way microphones with directional characteristic will change the sensory perception in a way that suggest both hands raised up to the ears to form an ear trumpet. In contrast to those animals with adjustable ear conches human sensory physiology can be considered as comparatively simple.

It follows, therefore, that sonic authenticity finally can be achieved only if the microphone characteristic and position emulate the transition from the “external” to the “internal” world of a person.

2. Fokussing and projektion

The eardrum is the physiological transition region from the acoustical “external world” to the perceptual “internal world”. All the sonic informations are channeled here. They focus effectively on this about 55 mm² membrane. That means in a figurative, technical sense a data compression, a reduction of an enormous amount of data into a physical very simple transfer structure. The physiotechnical unit tympanic/internal ear on the other hand spreads the Information losslessly by mechanical means for the genuine sensory-physiological reception where after all the final decompression, enhancing and contrast elevation of the “data” takes place.

3.Authentic recording and playback issues

From the above it is deduced that besides all the highly technical recording practice of today with all their methods of mixing and postprocessing there is an amazingly simple alternative: The acoustic event with all its spatial dimensions and all its high data complexity is to be tapped exactly in position of its physical simplest concretion. That is the position of the eardrum. Afterwards the recording will be reproduced precisely at this spot. Every commercial earphones of good quality will fit. The human sense of hearing takes care of the final processing. It is specialized by doing that. Not even the best sophisticated technical procedure would be close to the efficiency of human senses.

Since 1969 this principle for authentic recording and reproduction of sound and acoustics is called “Kunstkopf stereophony”. Beginnings of that idea yet trace back to 1886, when corresponding experiments had been presented at the first world exhibition in Paris. During the 1970^th in particulat German broadcasting stations used the Kunstkopf technology for experimental radio dramas and even for music recordings. But mainly due to the more or less on ear phones restricted playback options this technique had not been able to assert itself in the end.

Since then, the Kunstkopf technology has advanced primarily in the scientific field of noise measuring and sound analysis and we find it widely used in the industry. As by now the reproducibility of an authentic surround sound by loudspeakers has improved a lot by the use of a so-called crosstalk compensation the Kunstkopf again finds more and more application in the music production. It may therefore be the case that Kunstkopf stereophony will start a new movement of a conscious listening.