By Xavier Hautbois

The origins of the TSUs derive from an observation made by musicians
and researchers from the Laboratoire Musique et Informatique de Marseille (MIM) in 1991. While Schaeffer aims to describe sound through a morphological description based on a “limited listening” (to quote Schaeffer’s term), which consists in ignoring any causal or associative meaning, the composition of an electroacoustic piece appears to be quite far from such a practice. For example, French composers like Pierre Henry or François Bayle select their sounds and classify them according to their meaning, based on an associative denomination, on what the sound “tells” (i.e., “something in there had to seem to be singing to me”, Bayle, 1990). Therefore, the MIM researchers have proposed to reintroduce meaning in their description of sound objects and define some kinds of semiotic objects, called Temporal Semiotic Units. It should be emphasized that the MIM’s work is consistent with various empirical and theoretical approaches to classification based on time perception, used by composers like Salvatore Sciarrino (Figore), Trevor Wishart (Morphology of sounds), Denis Smalley (Spectromorphology), François-Bernard Mâche (Archetypes/Genotypes/Phenotypes), Costin Miereanu (Elementary Formal Categories) and François Bayle (Morphodynamic Categories). For all these composers, categories stem from their own auditory and compositional experience.

Assuming that some musical figures seem to produce both a specific
temporal meaning and kinetic effects, the research group looked for any remarkable dynamic or static sound effect (uniform or accelerated motion, circular or linear process, compression, propulsion or stationary state…) in a number of electroacoustic pieces. For example, let us consider the effect of the illusions induced in the auditory by Roger Shepard, as illustrated by Jean-Claude Risset in Mutations: it is a sound whose pitch continually increases or decreases and which ultimately does not seem to get higher or lower. These sounds have a precise single-stage temporal evolution. It is not the sound illusion that interests us here (tone appears to rise or fall without eventually changing in pitch), but the inexorable and predictable process related to the pitch parameter. This temporal process corresponds to a unified sound figure characterized by the MIM researchers as Endless trajectory. Another example is a two-phase sound figure frequently encountered in Bernard Parmegiani’s works (De natura sonorum), which is called Compressing-stretching out: the first fairly short phase including small accumulated and compressed sound elements is followed by a second period, opposite to the first and containing a consistent sound which slowly extends over time. Of course, this figure can be described in purely morphological terms but the impression that we get from the accumulation of sounds followed by an expansion over time, two phases constituting a coherent and complete unit, is exclusive to this temporal figure. Some morphological criteria must be observed to produce the effect (they are relevant morphological traits) while others do not make any difference (sound figures can be played in any register: low, middle or high), but it is clearly in the temporal meaning of the Compressing-stretching out or Endless trajectory that we can identify and isolate a unit. In this respect, they are Temporal Semiotic Units. TSUs have been defined as “musical segments that possess a precise temporal signification linked to their morphological organization” (François Delalande). In other words, TSUs are sound forms which convey meaning through their dynamic pattern over time.

TSUs are not Schaefferian sound objects because they are not isolated
from their context according to the same segmentation criteria (that is why the name of “semiotic object” was finally dropped). The Schaefferian sound object is extracted from its context in accordance with purely gestalt laws and not with meaning units like TSUs (in which a minimal segment corresponding to a well-defined meaning is searched). Thus the division of sound objects and that of TSUs do not necessarily coincide: a TSU can be made up of a set of sound objects.

In order to observe and list the different TSUs, the MIM researchers
first listened to a great number of musical works and then divided them into musical segments that have a precise temporal meaning. They are based on a listening attitude that focuses neither on the pitch of a note, nor on the musical harmony or timbre of sounds, but on the whole effect of all these parameters over time. The researchers gathered segments that had a similar temporal organization: each category has been described on morphological and semantic levels identifying relevant common characteristics. Four morphological characteristics have been used: duration, which can be time delimited (these TSUs are usually multi-phases with distinct beginning and end) or not (in which case, a portion of the unit is enough to identify the whole segment, like the Endless trajectory); reiteration (with cycles or not); number of phases (one or more) and sound matter (continuous or discontinuous sound). Two kinetic characteristics have been added to the previous ones: the acceleration type (positive or negative) and temporal progression (fast or slow). Several semantic characteristics are also provided like the process direction (one or more sound parameters moving in the same direction), movement (motion effects) and ultimately sound energy (constant or retained, for example). Every TSU has been analyzed according to these characteristics and given identification cards.

The MIM researchers have defined 19 TSUs so far, that they
have metaphorically called as follows: Braking, Chaotic, Compressing-stretching out, Divergent, Endless trajectory, Fading away, Falling, Floating, Heaviness, In suspension, Moving forward, Obsessive, Propulsion, Spinning, Stationary, Stretching, Suspending-questioning, Wanting to start, Waves.

We need to make it clear that the MIM’s research program is a
long-term work and that the solutions proposed today by these researchers must be considered as provisional and evolutionary ones. Indeed, since TSUs were empirically obtained from contemporary pieces of music (in particular electroacoustic music), there is no guarantee that no other TSU will be discovered in other unanalyzed works, in works from different musical styles or other musical cultures. A few TSUs are especially adapted to music from the second half of last century: such is the case, for instance, of the TSU Divergent (characterized by a succession of brief temporal sequences bearing no relationship with one another) or the TSU called Chaotic (it is a dense superimposition of musical sequences resulting in high saturation). But the MIM researchers have rapidly discovered that most TSUs had a more global scope fit for the analysis of varied repertoires.

Here are a few TSU identification cards and sound examples for each
of them: several musical excerpts, a piano improvisation and a sound synthesis according to the Parameterized Time Motifs model (which is a kind of abstraction of TSUs, their temporal skeletons).

Compressing - Stretching out :

Endless trajectory :

Obsessive :

Propulsion :

Spinning :

Waves :