This paper presents a compositional framework using Computer-Aided Orchestration strategies to position the evolution of timbre as the fundamental engine of musical morphogenesis. Moving beyond purely physical-acoustic modeling and the use of abstract parameters and timbral descriptors, the proposed method focuses on the semiotic and psychoacoustic dimensions of sound. It investigates how source sounds, selected for their evocative potential, are analyzed and orchestrated to implicitly recreate part of their original sensations through complex blended timbres and textures, thereby generating formal tension and structural progression.

The theoretical framework is twofold. First, it is based on the findings of McAdams and Giordano (2008) regarding timbral perception as a vector of musical tension. By selecting specific sounds for their semiotic or psychoacoustic charge (such as a baby cry, a rasgueado, or a church bell) and refining their orchestration through Computer-Aided Orchestration strategies (mainly through the use of the Orchidea software), I evoke the emotional and physical resonance of the original source without resorting to direct imitation. This process enables the musical form to emerge from the listener's psychological reaction to the sound's evolution.

Second, this research utilizes orchestral blend as a strategic tool for timbral de-identification. Grounded in Sandell's (1995) study of the spectral centroid and its role in determining blended pairings, I employ specific orchestration strategies to generate emergent timbres that transcend the recognizable identity of individual sound sources. By suppressing source identification, I maximize the perceptual distance between the acoustic generators and the resulting sonic object. This process is essential to my semiotic framework, as it allows the listener to focus on the evolution of texture and evoked sensation rather than the mechanical means of production.

The analysis of two recent works demonstrates these principles:

- Triptyque du cri (for an ensemble of eight instruments, including electronics): Here, diverse sonic sources are formalized along a pleasant/unpleasant axis. Computer-Aided Orchestration transforms these varied inputs into emergent instrumental textures that transcend their origins, building a structure based on the psychoacoustic resonance of the materials.

- Unplugged (guitar concerto): This work applies the concept of expansive orchestration to navigate the intentional difficulty of blending the guitar with the orchestra. This challenge, arising from the guitar's low relative volume and its idiosyncratic attack, is addressed by avoiding the traditional responsorial texture in guitar concertos, treating the ensemble as an extension of the soloist.

This research demonstrates how the convergence of semiotic intent and psychoacoustic analysis allows computer-aided orchestration to act as the primary architect of musical form through the creation of emergent sonic identities.

References:

- McAdams, S., & Giordano, B. L. (2008). The perception of musical timbre. In S. Hallam, I. Cross, & M. Thaut (Eds.), The Oxford Handbook of Music Psychology (pp. 72–80). Oxford University Press. https://doi.org/10.1093/oxfordhb/9780199298457.013.0007

- Sandell, G. J. (1995). Roles for spectral centroid and other factors in determining “blended” instrument pairings in orchestration. Music Perception, 13(2), 209–246. https://doi.org/10.2307/40285694