Tidal -- Pattern Language for Live Coding of Music
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TIDAL – PATTERN LANGUAGE FOR LIVE CODING OF MUSIC Alex McLean and Geraint Wiggins Centre for Cognition, Computation and Culture Department of Computing Goldsmiths, University of London ABSTRACT into a canon [3]. Hierarchies and heterarchies of repeat- ing structure run throughout much of music theory, and Computer language for the description of pattern has been computational approaches to music analysis, indexing and employed for both analysis and composition of music. In composition all have focus on discrete musical events and this paper we investigate the latter, with particular inter- the rules to which they conform [4, x4.2]. From this we est in pattern language for use in live coding performance assert that the encoding of pattern is fundamental to mu- [1]. Towards this end we introduce Tidal, a pattern lan- sic making. In the following we review support given to guage designed for music improvisation, and embedded in musical pattern making by computer language, and then the Haskell programming language. introduce Tidal, a language for live improvisation of musi- Tidal represents polyphonic patterns as a time varying cal pattern. Before that we motivate the discussion through function, providing an extensible range of pattern genera- brief review of the practice of live coding, for which Tidal tors and combinators for composing patterns out of hier- has been created. archies of sub-patterns. Open Sound Control (OSC) mes- sages are used to trigger sound events, where each OSC parameter may be expressed as a pattern. Tidal is designed 2. LIVE CODING to allow patterns to be created and modified during a live Since 2003 an active group of practitioners and researchers coded performance, aided by terse, expressive syntax and [5] have been developing new (and rejuvinating old) ap- integration with an emerging time synchronisation stan- proaches to improvising computer music and video ani- dard. mation; activity collectively known as live coding [6,1, 7]. The archetypal live coding performance involves pro- 1. INTRODUCTION grammers writing code on stage, with their screens pro- jected for an audience. The code is dynamically inter- When we view the composed sequence “abcabcabc. ” we preted, taking on edits on-the fly without losing process quickly infer the pattern “repeat abc”. This is inference state, so that no unwanted discontinuities in the output oc- of hierarchy aiding memory of long sequences, prediction cur. Here a software development process is the perfor- of future values and recognition of objects. Pattern per- mance, with the musical or visual work generated not by a vades the arts; as Alfred Whitehead [2] eloquently puts it, finished program, but its journey of development from an “Art is the imposing of a pattern on experience, and our empty text editor to complex algorithm, generating contin- aesthetic enjoyment is recognition of the pattern.” To our uously changing musical or visual form along the way. shame these words were background to Whitehead lam- A key challenge set to live coders is to react quickly in basting those taking quotes out of context, but nonetheless musical response to other performers, or else on their own communicate a role of pattern supported here; one individ- whim. This can be difficult due to a straight trade off in the ual encodes a pattern and another decodes it, both actively level of abstraction they have chosen; while a traditional engaged with the work while creating their own experi- instrumentalist makes one movement to make one sound, ence. In this paper we examine the encoding of pattern a live coder makes many movements (key presses) in order in particular, introducing Tidal, a computer language for to describe many sounds. It is in a live coder’s interest to encoding musical patterns during improvised live coding find highly expressive computer language that allows their performances [1]. ideas to be described succinctly. The subject of We believe Pattern is everywhere, and the subject of musical pat- the prese focus on the composition of pattern language pro- tern is a broad subject alone. The desire to capture musical vides a positive step in the right direction. patterns with machines goes back to well before electronic computers. For example, Leonardo da Vinci invented a hurdy gurdy with movable pegs to encode a pattern, and 3. PATTERN LANGUAGE multiple adjustable reeds which transformed the pattern Literature on pattern language is mainly concerned with analysis of composed works relative to a particular the- Copyright: c 2010 Alex McLean et al. This is an open-access article distributed ory of music. For example Simon and Sumner [8] pro- under the terms of the Creative Commons Attribution License 3.0 Unported, which pose a formal language for music analysis, consisting of permits unrestricted use, distribution, and reproduction in any medium, provided a minimal grammar for describing phrase structure within the original author and source are credited. periodic patterns. Their language allows for multidimen- sional patterns, where different aspects such as note value, systems are all inspiration for our own pattern language, onset and duration may be expressed together. The gram- introduced below. mar is based on a language used for description of aptitude tests which treat pattern induction as a correlate for intel- 4. TIDAL ligence. Somewhat relatedly, research has since suggested that there is a causal link between music listening and in- Tidal is a pattern language embedded in the Haskell pro- telligence [9], known as the “Mozart effect”. However this gramming language, consisting of pattern representation, result has proved highly controversial [10], and we would a library of pattern generators and combinators, an event certainly not claim that pattern language makes you clever. scheduler and programmer’s live coding interface. This Deutsch and Feroe [11] introduced a similar pattern lan- is an extensive re-write of earlier work introduced under guage to that of Simon and Sumners, for the analysis of the working title of Petrol [15]. Extensions include im- hierarchical relationships in tonal music with reference to proved pattern representation and fully configurable inte- gestalt theory of perception. gration with the Open Sound Control (OSC) protocol [16]. The analytical perspective shown in the above lan- 4.1 Features guages puts focus on simple patterns with unambiguous interpretation. Music composition however demands com- Before examining Tidal in detail we first characterise it in plex patterns with many possible interpretations, leading terms of features expected of a pattern language. to divergent perception across listeners. Therefore pattern language for synthesis of music requires a different ap- 4.1.1 Host language proach from analysis. Indeed, a need for the design of Tidal is a domain specific language embedded in the pattern language for music composition is identified by Haskell programming language. The choice of Haskell al- Laurie Spiegel in her 1981 paper “Manipulations of Mu- lows us to use its powerful type system, but also forces us sical Patterns” [12]. Twelve classes of pattern transforma- to work within strict constraints brought by its static types tion, taken from Spiegel’s own introspection as a composer and pure functions. We can however turn this strictness to are detailed: transposition (translation by value), rever- our advantage, through use of Haskell’s pioneering type- sal (value inversion or time reversal), rotation (cycle time level constructs such as functors and monads. Once the phase), phase offset (relative rotation, e.g. a canon), rescal- notion of a pattern is defined in terms of these constructs ing (of time or value), interpolation (adding midpoints and a whole range of cutting edge computer research becomes ornamentation), extrapolation (continuation), fragmenta- available, which can then be explored for application in tion (breaking up of an established pattern), substitution describing musical pattern. (against expectation), combination (by value – mixing/- Tidal inherits Haskell’s syntax which is both terse counterpoint/harmony), sequencing (by time – editing) and (thanks to its declarative approach) and flexible, for exam- repetition. Spiegel felt these to be ‘tried and true’ basic op- ple it is trivial to define new infix operators. Terse syntax erations, which should be included in computer music ed- allows for faster expression of ideas, and therefore a tighter itors alongside insert, delete and search-and-replace. Fur- programmer feedback loop more suitable for creative tasks ther, Spiegel proposed that studying these transformations [17]. could aid our understanding of the temporal forms shared by music and experimental film, including human percep- 4.1.2 Pattern composition tion of them. In Tidal, patterns may be composed of numerous sub- Pattern transformations are evident in Spiegel’s own patterns in a variety of ways and to arbitrary depth, to Music Mouse software, and can also be seen in music soft- produce complex wholes from simple parts. This could ware based on the traditional studio recording paradigm include concatenating patterns time-wise, merging them such as Steinberg Cubase and Apple Logic Studio. How- so that they co-occur, or performing pairwise operations ever Spiegel is a strong advocate for the role of the mu- across patterns, for example combining two numerical pat- sician programmer, and expresses hope that these pattern terns by multiplying their values together. Composition transformations