For the conference, which dealt with spatial models of timbre in the broadest sense, international experts could be found as speakers: Charalampos SAITIS, Maria MANNONE, Kai SIEDENBURG, Christoph REUTER, Dieter MAURER.
The topics and research questions of the conference ranged from psycho acoustic to technological and philosophical approaches to an aspect of sound perception which is sometimes called a “multidimensional dimension”. The fundamental categories of tone, colour, space, time and movement seem to evaporate when we try to fathom their essence. Derived notions such as time space, timbre (“sound colour”), hue (“colour tone”), tonal space and space-time are therefore not spared ambiguities and vagueness either. Whereas spatial models for pitch (“tone height”) have a long history, to date no reliable spaces for timbre could be established unequivocally. Although the timbre space metaphor conjectured by John Grey and the visualisations from his writings (1977/1978) are depicted in many introductions to musical acoustics, timbre is far from being a universally valid spatial feature of musical sounds.
Changes in the frequency content of sounds over time are arguably the most basic form of information about the behavior of sound-emitting objects. In perceptual studies, such changes have mostly been investigated separately, as aspects of either pitch or timbre. Here, we propose a unitary account of “up” and “down” subjective judgments of frequency change, based on a model combining auditory correlates of acoustic cues in a sound-specific and listener-specific manner. To do so, we introduce a generalized version of so-called Shepard tones, allowing symmetric manipulations of spectral information on a fine scale, usually associated to pitch (spectral fine structure, SFS), and on a coarse scale, usually associated timbre (spectral envelope, SE). In a series of behavioral experiments, listeners reported “up” or “down” shifts across pairs of generalized Shepard tones that differed in SFS, in SE, or in both. We observed the classic properties of Shepard tones for either SFS or SE shifts: subjective judgements followed the smallest log-frequency change direction, with cases of ambiguity and circularity. Interestingly, when both SFS and SE changes were applied concurrently (synergistically or antagonistically), we observed a trade-off between cues. Listeners were encouraged to report when they perceived “both” directions of change concurrently, but this rarely happened, suggesting a unitary percept. A computational model could accurately fit the behavioral data by combining different cues reflecting frequency changes after auditory filtering. The model revealed that cue weighting depended on the nature of the sound. When presented with harmonic sounds, listeners put more weight on SFS-related cues, whereas inharmonic sounds led to more weight on SE-related cues. Moreover, these stimulus-based factors were modulated by inter-individual differences, revealing variability across listeners in the detailed recipe for “up” and “down” judgments. We argue that frequency changes are tracked perceptually via the adaptive combination of a diverse set of cues, in a manner that is in fact similar to the derivation of other basic auditory dimensions such as spatial location.
Artists are at ease with the complexity of timbre in orchestration and color in the visual arts. However, timbre and color are different phenomena in physics. Timbres result from the superposition of sinusoidal signals of longitudinal acoustic waves. Colors come from the superposition of transverse electromagnetic waves of visible light.
Colors and timbres have in common the idea of superposition, and their variations in some cases produce a similar perceptive effect in humans. We describe a recent experiment in this domain. Then, we describe perceptive similarities with definitions and tools of category theory. We define categorical groupoids, having as objects the colors (or timbres) and, as morphisms, color variations (or timbre variations). We model comparisons between colors and timbres via functors.
Finally, we present some case studies where timbres convey information in sonification, from sonified medical data to robotic movement feedback. Timbre-related sensitivity allows us to distinguish elements in a sonification, shape information such as the age of patients in a medical study, or help characterize the different robots of a swarm and their movements.
Timbre is a perceptual property of sounds, encompassing a complex set of attributes collectively contributing to the inference of a sound’s source but also acting as qualia. Typically, timbral qualities of sounds are verbally communicated through descriptions such as bright, rough, or full. There is converging evidence that timbral vocabularies can hold intersubjective reliability and are constrained by discrete conceptual-metaphorical schemas. These metaphors we listen with are not crucial for perceptualising timbre—one can compare and recognize timbres without having to tag them verbally—but are central to conceptualising timbre by allowing to make sense of its perceptual representation through indexing other, more commonly shared semantic representations. A major body of studies have sought to construct “semantic spaces” of timbre. These are geometrical configurations resulting from factor analysis of stimuli ratings along semantic scales. This approach has contributed greatly to our psychoacoustical understanding of timbre, but the broader cognitive questions concerning the ability of the human brain to draw metaphors across sensory and other experiential domains are far from trivial. In this talk, semantic spaces of timbre are examined in the context of Gärdenfors’ theory of conceptual spaces, a framework for representing information on the conceptual level based on geometry, and vice versa.
Timbre can be described using various methods. One popular method is the use of timbre spaces, which plot the spectral characteristics of a sound in a mostly three- or four-dimensional space. However, these spaces have limitations and cannot be easily compared or generalized. Another method, Mel Frequency Cepstral Coefficients (MFCCs), has proven to be effective but the MFCCs are not particularly intuitive. Formants as pitch-independent maxima in the spectrum of an instrument's timbre with a defining effect on its overall character are less universal than MFCCs and also cannot be applied equally to all musical instruments. However, in the low and middle registers of most musical instruments they are easily recognizable and thus very intuitive, generalizable and easy to understand. Instruments with similar formant ranges tend to blend well together, while those with different formant ranges may not. Formants have been somewhat overlooked in English-language literature, but they have the potential to be useful timbre descriptors. In this contribution, various types of timbre spaces and formant maps are presented, including interactive versions and formant maps that show timbre changes over the course of a musical piece.