We experienced that after having provided few information about the “sound sheet” and some commented examples, acousmetric shapes (such as dot, line triangle, square, pentagon, circle, etc.) are easily recognised and graphically reproduced by the listeners [1].

As any other code, acousmetry requires a learning phase (in this case really short). Children learn at the school to recognise a triangle, to distinguish between an “A” and an “I” and to reproduce different sound as correspondences; we learn foreign languages through laborious mnemonic exercises; a musician can recognise a 7^thdim chord after a heavy and long training of the musical code; all these examples impose a linguistic context as a common reference.

We are verifying the acousmetric perception through tests submitted to statistical analysis: the tests consist of listening sample acousmetric shapes, and of drawing the corresponding graphics on a paper; the data presently available are under process, but the high percentage of positive results already can convince that everybody can perceive acousmetric shapes, and that the phenomenon is general.

Acousmetry is a discipline rigorously formalised, according with three parameters, we refer to the three spatial co-ordinates:

Right-left. The diffusion of stereophonic recordings made us used to perceive sound on a left- or rightside; a continuous shift of the balance from left to right is felt as a sound dot moving in the same direction.

Front-back. The perception of the depth (near-far) with two loudspeakers appeals to linguistic metaphors and to experiential interpretations, and two mechanisms apply for still or moving sources.

Still sources: our experience says that weak signals come from far sources; more we have a model describing mathematically the phenomenon: the intensity of the perceived signal decreases with the square of the distance; we can control the loudness of a signal following the above law, in order to represent the required spatial distance.

Moving sources: for low speeds, the above considerations on still sources apply; for fast speed, the Döppler effect can be used, increasing the frequency of the sounds coming toward us and decreasing it for sources going away from us.

The mechanisms are in the hands of the acousmetric composer: if the goal is the representation of a central far source approaching fast the listener, he will provide a central sound, initially weak, becoming louder and louder while increasing in the pitch. Possible ambiguous representations shown that the listener chooses the simpler to be interpreted [2]:

F.i., with two loudspeakers, if a central weak sound grows in volume and pitch till a maximum for returning then to initial volume and pitch, a listener positioned in the mid point between the two speakers could interpret it as a sound dot coming from far and returning back or as coming from far and going far behind him.

According to a principle of continuity, the listener prefers feel the second solution.

The parameters of such a sound can be physically modelled as shown in fig.2, supposing a listener centered between the speakers and looking toward the front part:

Fig. 2 – Depth perception through Volume and Pitch control

A listener in the same position but looking in the backward direction will feel the same phenomenon: the sound coming from far in front to him and moving away back.

While the perception left-right corresponds to the real physical phenomenon (the sound comes from left or right, or the ears process the position according to the average of the intensities coming from left and right; we can measure in meters th distance between the speakers and express in meters the position of the sound), the perception far-near, coming-going are ruled by “state variables”: they are meaningful only in a comparison (3).

High-low. The use of two speakers only allows the perception of high and low position through metaphoric linguistic mechanisms. The terms “high” and “low”, “up” and “down”, are really powerful in the day by day communication: we go down the stairs or up at home (real physical interpretation), but the stock exchange is going up or down, we say “up with the people”, “I’m down today”, and so on.

The same metaphor is used in music, with sounds going up (pitch) and becoming high, or goes down becoming low. A sound coming from the left speaker increasing continuously its pitch is interpreted as dot spatially rising on the left party of our sound sheet. The reverse for dots moving down.

Acousmetry formalises the correspondence sound – shape; f.i. we could model the gesture of a diagonal segment from the lower left corner to the upper right as a couple of coordinates changing in the time:

x = kt               y = kt

and the corresponding acousmetric shape will map x on the speakers balance, and y on the pitch [4]. The process is invertible (in a mathematic sense, and an acousmetric shape generated starting from a geometric one can be examined to re-generate the original gesture.
Acousmetry is a new discipline, and there are few examples of its use in various fields (marketing, arts, museum and fair settings, architecture, design etc.); leaving to the references [4] the details, we will give in the following examples of application in arts, and report here below an example of an acousmetric brand (the figure represents the wave form of the big red “i”).