Timbre space representation as a tool for conceiving of how to compose with or analyze timbral structures David Romblom, Gabriel Vigliensoni Music Technology Area Schulich School of Music McGill University Outline Timbre space introduction Technique in modern music Technique in computer music Navigating timbre space Technique in modern music production Timbre space introduction Summary of general timbre space generation method Timbre space represents the geometrical organization of perceptual distances, measured in dissimmilarity ratings, between tones with equal pitch, loudness and perceived duration. Selection of materials for study Collection of (dis)simmilarity judgements Representation of the (dis)simmilarity judgements Psychoacoustic interpretation of the structure Verification of the structure in musical situation Perceptual e!ects of spectral modifications on musical timbres (Grey and Gordon, 1978) An original timbre space was defined using 16 synthetic tones and MDS methods. (Gordon and Grey, 1977) A second study was conducted, where 8 of these tones swapped spectral envelopes. (Gordon and Grey, 1978) All of the swapped tones also swapped places in the timbre space. Big deal: modifications to acoustic descriptors cause predictable and meaningful perceptual changes. This opens the door for meaningful operations on timbre, we can modify descriptors and get (hopefully) musically useful results! Perceptual scaling of synthesized musical timbres: Common dimensions, specificities, and latent subject classes (McAdams et al., 1995) A data set of timbre dissimilarity judgements was analyzed using the CLASCAL MDS method to have five classes of subjects, called latent classes. The first two classes weighted all of the dimension approximately equally, meaning that the dimensions were roughly equal perceptually. The other classes did not, indicating that some dimensions were perceptually “heavier” for them. Big deal: timbre space might be an individual perception in some cases. Musical training didn't matter as much as one might guess. Everybody uses timbre every day to “figure out what is going on out there.” Big deal: timbre is important to everybody, as such, musicians should be using it! Specificities are acoustic qualities specific to a given instrument. Considering these in the analysis allowed a reduction from: 6 hard to interpret dimensions to 3 psychophysically meaningful dimensions: log-rise time, spectral centroid, and spectral flux. Big deal: this means 3 dimensions might be enough to “get around” in timbre space. Acoustic correlates of timbre space dimensions: A confirmatory study using synthetic tones. (Caclin et al., 2005) Aim Participants Stimuli Statistical Analysis Results To determine if the structure of the perceptual space is closely parallel to the acoustical space, particularly using attack time, spectral centroid, spectral flux, and attenuation of high harmonics as the physical dimensions. What is the auditory mapping between the physical parameter and the perceptual values 3 experiments, 30 subjects musicians and non-musicians 16 synthetic tones, perceptually equalized in duration and loudness, homogeneously distributed in space variations in the attack time (log steps), SCG (linear steps), spectral fux (equally spaced steps) Outliers data discarded Dissimilarity ratings analyzed using CLASCAL and CONSCAL MDS models Attack time and SCG were confirmed as salient timbre parameters, but spectral flux was not used in dissimilarity ratings when attack time and SCG varied concurrently. The experiments shed new lights about possible third dimensions of timbre spaces, but the type of spectro-temporal information that listeners use remains unclear. The items conserve their position along the perceptual dimension, but their actual position is derived from the physical values by a continuous monotone spline function which is di!erent for each person In other words, people hear music in di!erent ways. The Timbre Toolbox: Extracting audio descriptors from musical signals (Peeters et al., 2011) Aim To provide a comprehensive set of audio descriptors to perform perceptual research. Analysis Corpus of 6037 pitched and non-pitched sounds Technique Results For assesing the redundancy of information of the descriptors, an experiment was developed to found their correlation, thus allowing the selection of the most independent ones. 53 audio descriptors for capturing the temporal, spectral, spectro-temporal and energetic–global or time-varying–characteristics of the set of sounds. Descriptive statistics for characterizing time-evolving descriptors Correlational analysis and hierarchical clustering in the set of descriptors is performed for examining the information redundancy The analysis suggests ten classes of relatively independent audio descriptors The toolbox is a multidimensional instrument for the measurement of the acoustical structure of complex sound signals Technique in modern music “If it is possible to make compositional structures from sounds which di!er according to pitch, structures which we call melodies, sequences producing an e!ect similar to thought, then it must also be possible to create such sequences from the timbres of that other dimension from what we normally and simply call timbre. Such sequences would work with an inherent logic, equivalent to the kind of logic which is e!ective in the melodies based on pitch. All this seems a fantasy of the future, which it probably is. Yet I am firmly convinced that it can be realised.” (Schoenberg, 1911:470-471) J.S.Bach 'Ricercare a 6'. BWV 1079 (scores taken from Erickson, 1974) Gestalt timbre: Individual timbres are part of a whole Cogan and Escot uses the spectrogram to study timbral orchestration (Sonic Design, 1976) (Slawson, 1985) Technique in computer music “Though more research needs to be done, the notion of transposing a sequence of timbres by forming another sequence geometrically parallel to it in timbre-space thus appears to be a reasonable and musically viable idea.” (Wessel, 1979) McAdams and Cunible (1992) show the validity of timbre analogies, suggesting that timbre could be subject to musical operations. Similar to intervals in pitch and in time, the sucession of intervals in timbre space defines a timbre melody Vectors through timbre space - Technique in MDS As sounds are located in the timbre space, we can think of timbre intervals as vectors in the timbre space, and we can apply cartesian operations on these vectors. However, some questions arise: What is the minimum distance interval (a.k.a. 'the semitone') in terms of timbre? Does that distance change per dimension? What is the role of rotation? Is the 2" spiral the timbral octave? Could we develop a symbolic notation for timbre? Pitch technique of the Western Art Canon can be extended Chromatic transposition adds a fixed intervalic o!set to every pitch class. Diatonic transposition adds the same interval class to every pitch class Chromatic inversion is the negation of the pitch intervals, as measured in semitones. Diatonic inversion is the negation of the intervalic class. Contour mantains direction, but manipulates the size of the intervals Sticky Points Timbral glissando, or discrete steps? What does diatonic mean in the context of timbre? It seems that chromatic and modern set theory techniques are most appropriate! Transposition = O!set Take a given vector path in timbre space, and move it to a new starting point Inversion = negate a dimension Take a given vector path in timbre space, and negate one, many or all dimensions. Note the possibility of a partial inversion – this is novel to timbre! Contour = scaling Scale any given dimension Tension and release Tension based upon psycho-acoustics – amount of information and auditory roughness. If tension in timbre is achieved through roughness, is release achieved through auditory smoothness? Release might be more than simplicity, sine tones are smooth but unpleasant. In equal tempered music, certain intervals have certain tendencies, e.g., the dominant seventh chord 'points'. Such parallels are not clear in common practice harmony, however. Perhaps only the very general parallels to tension and release (of modern harmony) are valid. Hyper-timbres It would be interesting to think about extreme, hyper timbres because they could define, limit our sonic working space. What are the extreme sounds that we could generate in a timbre space? Are the impulse and silence located at the boundaries of the timbre space? Does the timbre space have boundaries? Would it be possible to go beyond the boundaries of a timbre space? Discrete vs. Continuous 'Common practice' instruments are clustered in the timbre space. Here, categorically identification may actually impede the use of timbre as a compositional tool! Instead of hearing smooth transitions, temporal/timbral segmentation wrecks the intended timbre melody. Modern composers began working with blend to 'work around' this problem. Synthethic sounds can be manipulated to fill the space continuously – the sky is the limit. Music for 18 musicians, S. Reich Musical Analysis of Timbre Structures It has been common in the western art tradition for music theorists to analyze the vocabulary of the accepted masters of composition. In acoustic music up to the modern masters, an analysis of pitch and duration can be derived from the score or by skilled ears. An analysis of categorical timbre can also be derived from either the score or by ear – it only answers the question of what instrument played what part. Scientific analysis is more di#cult, especially once all of the parts are combined into a given recording. The spectrogram tools suggested by Cogan and Escot (Sonic Design, 1976, Slawson 1985) allow us to view the timbre structure at a very high level, but would be unlikely to reveal anything similar to a timbre melody. The problem is similar in computer and electro-acoustic music, but is confounded by the extension of music beyond the note. Skilled ears might be able to detect patterned timbre composition in these works, whereas spectrogram tools will give a general outlay of the piece's overall timbre structure. Finer grained analysis tools might give more insight into fine grained structures, however a theory of analysis is not yet obvious. Navigating timbre space Étude des 1000 collants Karlheinz Stockhausen (1952) Open John Oswald ‘Plexure’ (1993) Music to observe electronic sheep to Part I Sven König (2006) Designing control systems from the perceptual representations “The timbre space representation suggests relatively straightforward schemes for controlling timbre. The basic idea is that by specifying coordinates in a particular timbre space, one could hear the timbre represented by those coordinates.” “The most natural way to move about in the timbral space would be to attach the handles of control directly to the dimensions of the space.” (Wessel, 1979) Frelia Mandel and Momeni (2005) CSS Technique Concatenative sound synthesis techniques allow a user to segment a collection of sounds into small units, analyze their sonic identity by means of the extraction of their acoustic and perceptual features using descriptors, and arrange the sound units into a multi-dimensional descriptor space according to their values. By means of the manual or automatic selection of sound units from the database and their concatenation, we can synthesize new sonic textures. CataRT (Schwarz et al., 2006) CataRT (Schwarz et al., 2006) TimbreID (Brent, 2010) SoundCloud (Vigliensoni, 2011) SoundCloud extends the interaction possibilities of previous concatenative sound synthesis systems by mapping the three-dimensional performance space to a threedimensional user-defined descriptor space. The system allows a musician to perform with a corpus of sounds distributed in a three-dimensional descriptor space by exploring a performance space with her hands. SoundCloud (Vigliensoni, 2011) ArcSyn (Romblom, 2007) ArcSyn attempted to put timbre on the same footing as pitch and loudness for performer: "For dynamic evolution, Arcsyn uses both ! and pp steady-state spectral information. Spectral morphing is achieved by adding a second, entirely distinct timbre with its own spectral information. The third dimension of interpolation is pitch; here we specify new spectral information at each welltempered note." The spectral database was packaged as an "analog oscillator" with dimensions of dynamics, timbre, and pitch. Technique in modern music production Technique in modern production Some of the main ideas in timbre research are well represented in modern music production. In particular, the timbre space axes are related to popular forms of signal processing: compressor/expanders, equalizer, non-linear distortion, and envelope followers. Axis 1 of many timbre space representations is log-attack time. This is related to compressor / expanders, which manipulate the onset and sustain of instruments. Axis 2 of many timbre space representations is spectral centroid. DAWs and mixing consoles provide equalizers and filters for modeling the spectral shape of a sound and changing its centroid. This processing technique allows producers to give instruments and sounds their own frequency space to 'cut' in the mix. Multiples timbres give rise to an overall timbre - Gestalt timbre! We have speculated that timbral tension results from auditory roughness. Nonlinear distortion creates new partials, many times no longer harmonic. This gives rise to beating and auditory roughness. Envelope followers allow producers to give more life to dull sounds by changing their spectral flux. Technique in modern production The backbeat is a timbre interval, and it is omnipresent in popular music. Second only to vocal treatment, the drum treatment is the next most important production element in most genres. Timbre matters: changing drum tones can alter the entire meaning of the song. Wrap and Summary Perceptual Issues our perceptual auditory system is adaptive di!erent sound stimuli arise di!erent timbre spaces flexible, adaptive strategies for working with timbre all reviewed experiments used isolated sounds no context was considered does context a!ect our timbre perception our perceptual dimension weighting and mapping is unique all of us listen di!erent common ground of timbral perception Syntactic Issues music is structure music is context define minimum, constituent parts to create the whole "If the timbral di!erence between adjacent notes is large, then one tends to perceive interleaved descending lines formed by the notes of the same timbral type." (Wessel, 1979) Wessel demonstrated that auditory stream formation and rhythmic organization of klangfarben sequences could be predicted from a timbre space. timbre space depends on the context timbre space is non-linear unified timbre theory COMPOSERS: TIMBRE MATTERS! THANKS!
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