Lsl.lpsr: applying contemporary compositional processes into an electro-acoustic improvisation tool
ABSTRACT Lsl.lpsr is an electro-acoustic improvisation tool inspired by Philippe Hurel’s Loops-compositions. The composi-tional process in these works results out of a synthesis be-tween spectral music’s continuous transformation and classical variation techniques. It defines a specific process for gradually transforming different musical parameters in repeated cells in order to create multi-layered ‘loops’-structures. This paper explains how lsl.lpsr implements these processes in a generative sequencer, thus allowing similar transformations and structures being created in real-time improvisation. Up to 8 independently running and self-transforming patterns generate the system’s out-put, while the performer can influence the direction of the transformations on different levels in the structural hier-archy. Using musical notation allows for displaying highly complex time relations and rhythmical structures in and between the patterns, but also enables operations such as metric modulations and phase-shifting. Lsl.lpsr can be used as both a MIDI sequencer and a live sampler.
1. INTRODUCTION As a percussionist I highly enjoyed performing the mu-
sic of French composer Philippe Hurel (°1955). His style is described as ‘Gérer l’Héterogène’ [1], creating a synthe-sis between spectral music’s continuous transformation and classical variation techniques. Hurel explicitly ex-plores this ‘loops’-process in his five ‘Loops’ composi-tionsi, and he inserts it regularly in his other compositions.
Fascinating as it is to perform the loops-process in composed music, it appears to be unsuited for convinc-ingly integrating it into acoustical improvisation. This is in line with theory of cognitive load: our long-term memory is capable of storing processed material, but working memory can only hold information from the sensory input for a short time span and only processes a few pieces of material at any one time [2, 3], making it impossible to re-tain and recall a stack of improvised transformations on the fly.
This paper explains how lsl.lpsr uses the loops-process in a generative sequencer, making it available for improv-isation. First, the loops process is introduced. Next, the pa-per describes the implementation of this process in the Max-patch. Specific attention will be drawn to the per-former’s role in creating ‘loops’-structures by manipulat-ing the transformations on different hierarchical levels. It will be clear that the use of musical notation not only clar-ifies displaying complex time relations and rhythmical structures, but also guides the system’s decisions and ena-bles operations such as metric modulations and rhythmical phase-shifting. Finally, the paper will illustrate a flexible way to use the system’s output simultaneously for gener-ating MIDI and for manipulating live-audio and samples in combination with M4L-devices.
2. THE LOOPS PROCESS
Table 1: transformations in the loops-process
The loops-process defines a specific way in which differ-ent musical parameters gradually transform during the rep-etition of musical cells. A motif - or its residue - launches a succession of transformations acting on each parameter differently. Their evolutionary direction marks them as constructive or regressive. These transformations are grad-ual and fragmented, thus always referring to the former motif within a constantly changing musical evolution. This creates a tension between fast and quasi-repetitive move-ment on the micro-level and slow continuous transfor-mations on the meso-level. Connecting these transfor-mations creates overall ‘loop’-structures on the macro-level [4, 5]. Table 1 provides an overview of these trans-formations for different musical parameters.
3. IMPLEMENTATION IN LSL.LPSR Lsl.lpsr contains 8 independently running and self-trans-forming patterns, which produce output and capture
changes. The performer influences how each pattern should transform itself on different structural levels. Changing settings for a parameter in a single pattern cor-responds to transformations on the micro-level, which guide the evolution of general characteristics rhythmic density, dynamic content, pitch content and curve. But the performer can also decide on the constructive or regressive direction for these general characteristics for a (selection of) pattern(s) or for the whole system. This puts his deci-sions on the meso-level, while the system will take care of the micro-level. Finally, the performer can rewind the transformation in each pattern, which applies all generated transformations in reversed polarity, thus creating a typical ‘loops’-structure by returning the pattern to its initial state. At each moment, the performer can also manually apply direct changes to the micro-level. These interventions will influence how ongoing transformations might evolve.
3.1 Micro-level patterns and alterations
Figure 1: single pattern with beats 3-11 selected. Se-
lected beats are colored differently.
A single pattern, such as displayed in figure 1, contains 16 beats with independent step-length, pitch, velocity and subdivision for each beatii. Pitch and velocity are MIDI values, with velocity – visualized as color intensity – scaled by an overall gain value. A rest indicates a muted beat. Each beat’s step-length is displayed as a rhythmic value with up to 16 subdivisions. A float and a rhythmic value represent the pattern’s tempoiii.
Standard -n, -nd and -nt suffixes indicate rhythmic val-ues, extended with -nq, -ndq, -ns and -nds for respectively quintuplets (5:4 and 5:6) and septuplets (7:4 and 7:6). Combined with numeric values (1, 2, 4, 8 … 128) they generate the beat’s multiplier. This multiplier is applied to the pattern’s tempo, which is the product of the tempo-float and its own rhythmic multiplier. The product of beat and tempo results in the beat’s frequency for the pattern’s internal timing-signal. The beat’s frequency is multiplied with the subdivision number for generating ramps which produce lists with the beat-number, length, pitch, velocity and mute information. It is important to note that pitch and velocity are tied to the beat; each subdivision of that beat will have the same information, but with reduced length.
Although manual changes to a (selection of) beat(s) or to a pattern’s range, tempo and gain are always possible, a pattern may also alter its own values generatively accord-ing to the performer’s restrictions, which are set with the alter-section as shown in figure 2. These restrictions are specified for each beat separately and contain:
- Outer limits of absolute parameter values - Alteration method (random or gradual) - Alteration speed (12-1) - Alteration direction (up/down/both) and type - Steps allowed in a single alteration (1-16)
The gradual method is specified to end or to restart after all beats have changed once. Speed selects a list-valueiv, indicating after which number of beats an alteration should be triggered. Steps limits the possible leaps. If both direc-tions are selected, type optionally specifies if alterations should proceed centrifugal or centripetal. These re-strictions are available for each individual parameter.
The restrictions are determinant in simulating the loops-process. For example, in pitch changes, direction up or down corresponds to constructive or regressive melodic range alterations, while convergent or divergent types cor-respond to altering the register and the melodic curve. Re-stricting steps provides strong coherence in the alteration process. By carefully choosing the alteration’s speed and method, the performer can simulate the quasi-repetitive character of transformations and retain the reference to the previous ‘situation musicale’ [1] in each repetition of the pattern.
Figure 2: Alter section for pitch. Steps here are re-
stricted to 1, 2, 3 or 12 semitones, parallel to ‘Loops II’
3.2 Rhythmical notation
For centuries, traditional occidental musical symbols mainly focused on binary or ternary time-divisions. As from the 20th century, composers focused on the emanci-pation of rhythm and meter. They introduced more com-plex time-relations, including expanded polyrhythm and -meter, irrational meters, metric modulationsv or simultane-ous tempo-independent parts [6]. The use of rhythmic no-tation creates interesting opportunities for applying these and other time-operations within a sequencer.
It is important to note that the -q and -s suffixes only indicate a single note in a tuplet, in contrast with a subdi-vision, which plays a specified number of attacks. How-ever, a combination of both systems allows to create for example a quadruplet on a beat with the length of a single quarter-note-triplet, as is the case on beat 13 in figure 1. When this beat alters to a quarter note, the quadruplet be-comes spread over a slightly longer timespan. Addition-ally, one can also spread a complete tuplet over individual beats. This not only allows for assigning individual pitches, velocities or rests to each element, but also makes them available for altering their length separately. A six-teenth-note-quintuplet could for example evolve over a number of repetitions into a combination of thirty-second and dotted-sixteenth notes. The performer can select which type of rhythms are available as steps. When a note-alter-ation is triggered, the system steps recursively through the rhythm-list until it reaches the next available note or limit.
Splitting the tempo into a float and a note-component allows for both fine-grained and metrically related tempo-changes. Assigning individual tempi to the patterns origi-nates in interesting ways for connecting them. Assuming two identical patterns, using the float component with slightly different tempi results in slow phase-shifting as
made famous in Steve Reich’s early worksvi. Equal float numbers with different rhythmical values construct poly-meters, while altering the rhythm-value for a pattern will result in a metrical modulation. When altering the rhythm of a single beat in one pattern momentarily, immediate phase-shifting of two patterns will occurvii. Altering the range of a pattern, creates additive and subtractive rhyth-mical operationsviii.
When using non-identical patterns, the same operations might happen. Simultaneously running patterns will often be perceived as – strongly or weakly – related [7]. When altering time-related parameters, the pattern’s mutual rela-tion will change and might lead to one of the temporal con-nections described above. Although these timing opera-tions are not new to contemporary nor electronic music, it is worth noting that using musical notation in lsl.lpsr makes them easily available in real-time for electro-acous-tic improvisation.
3.3 Meso-level characteristic transformations
Automatically transforming musical parameters liberates the performer from manually enforcing each discrete alter-ation in a single pattern. However, the combination of mul-tiple simultaneously transforming patterns then still re-quires a large amount of attention to the micro-level. While amid a performance, it could be more rewarding to shift one’s attention to the meso-level and make decisions on the direction of more general concepts. For that reason, lsl.lpsr combines multiple parameters in four general char-acteristics: density, pitch content, dynamic content and curve. Each characteristic is observed on a scale between 0 to 1.
Density represents the frequency of individual attacks. It combines the beat-length (rhythmic value and pattern tempo), subdivision and rest-state of all active beats. As changes in very short beat-lengths are less perceptible, density value is measured on a logarithmic scale. Pitch content takes pitch and rest-state of active beats into con-sideration on a linear scale. Similarly, dynamic content uses all active beat’s velocity and rest-states in combina-tion with the gain value. Curve calculates the capricious-ness of a pattern by evaluating the jumps from one active beat to the next. Obviously, muted beats are not taken into consideration.
The performer has the choice to guide these character-istics in a constructive or regressive direction by providing a target value for a characteristic. The system evaluates the current state and enables the proper alter-settings for the parameters involved. Once the target value has been reached or crossed, it will respectively disable or invert the alter states. The speed settings for the individual parame-ters will decide on the frequency for a certain alteration to happen, thus representing its weight in the overall proceed-ing of the transformation.
At this point, it becomes interesting to note how micro- and meso-level intertwine. When the performer launches the transformation for a characteristic, he might at any time intervene and change a certain parameter manually. The characteristic’s value will adapt accordingly and influ-ences the ongoing transformation. For example, manually muting beats in a pattern, changes the value for each
characteristic. If dynamic content is transforming, this might cause previously diminishing beats to start increas-ing in loudness, because the target value is suddenly higher instead of lower. On the level of density, this could force remaining beats to get smaller in length and to adopt more subdivisions in order to reach the target value. But also without manual interventions the transformations are in-fluencing each other: a change in pitch content will influ-ence the curve, or the alteration of the pattern’s range by the curve characteristic will cause all other parameters to re-evaluate their current actions.
3.4 Macro-level decisions
Lsl.lpsr also evaluates the characteristics of the patterns on the level of the whole system. Here again the performer can decide to let the entire system evolve towards a certain state. All currently running patterns are taken into consid-eration for calculating the main value, but only specifically selected patterns can be controlled to evolve in a certain direction. When a certain (un)selected pattern is manually changed or alters its own content, all selected patterns will be forced to respond to the new overall context.
All alterations in an individual pattern are stored con-secutively. The performer has the opportunity at each mo-ment to reverse the transformations. The pattern will then loop backwards through the list of alterations and reverse their polarity. If the individual settings of the pattern nor the overall settings of the system have changed, this will eventually result in a return to the pattern’s initial state, thus creating a circular macro-structure as is found in the separate movements in the ‘Loops’-compositions. How-ever, if the available rhythms have changed or the pattern’s limits have been adjusted, previously valid changes could be clipped differently or be evaluated as invalid, causing the pattern to arrive at an alternative state.
4. MIDI AND LIVE SAMPLING Lsl.lpsr outputs the generated data as MIDI or as a speci-fied list for dedicated audio players. In case of the latter, two M4L-devices are required: the recording device (fig-ure 3) operates autonomous to write audio into a specified buffer. It can record or overdub a single take or continu-ously rewrite its content. The player device (figure 4) op-erates in combination with lsl.lpsr and reads audio from the selected buffer based on the data received.
The recorder holds similar tempo- and beat-rhythm se-lectors as a pattern, but in this case, they are multiplied with Live’s tempo to calculate the size of the buffer. The player divides the buffer in 16 equal steps and plays the step which corresponds to the current beat-number. The performer can select an envelope for the step and set the direction: forward, backward, alternating or random. The velocity value decides on the playback volume, while the pitch value will produce a pitch-shift. The latter can be re-duced to less than 100% for micro-tonal results. Corre-spondence with lsl.lpsr happens via UDP. The ID-dial sets the port number where it will receive its notes. If an iden-tical note in the same tempo is received, the step will be played in its original length. When a non-identical note and/or a different tempo is received, the step will be
stretched or compressed accordingly. Each of the 16 steps can be manipulated independently.
Figure 3: M4L recorder Figure 4: M4L player
It is important to note that a pattern in lsl.lpsr is not connected to a fixed output. The pattern produces beat-lists and note-lists which contain data on length, subdivision (only beat), pitch, velocity and rest-state. The performer can route the output of each pattern to the 16 available MIDI-channels and 16 UDP-ports. This implies that one pattern can feed multiple virtual instruments and/or differ-ent player-devices, but also that one instrument or player can accept notes from multiple patterns simultaneously. In other words, a pattern functions just as a score for human players: multiple players can read from the same score, or the player can – theoretically – read a score with up to 8 independent voices. The performer then acts as an instant orchestrator, assigning musical material to different instru-ments in real-time. Similarly, the recording- and player-devices can switch buffers at each moment, allowing a flexible way of changing the content of the sampler and creating new sounds with the already constructed musical material. Figure 5 provides an overview of lsl.lpsr’s graph-ical user interface, including 8 patterns and their alter sec-tions, router windows and general controls.
5. CONCLUSION In this paper I introduced the Loops-process and discussed its implementation in a flexible and powerful improvisa-tion tool. I illustrated how this allows a performer to im-provise with the loops-process on different structural lev-els, and along the way I showed the importance of using contemporary rhythmic notation. It is worth noting that this decision also extended the system’s possibilities with other contemporary compositional processes, such as phase-shifting or metric modulation. I concluded with an overview of the routing options which allow the performer to apply the outcome of the generative patterns in a flexible way to multiple virtual instruments or live samplers in real time. Future development for the system includes improv-ing the analyzing capacities of the system and extending its possibilities to include manipulating visual input.
Although lsl.lpsr does not introduce new compositional processes, it makes them easily available in an electro-acoustic improvisational context. In this way, it forms a natural extension of my practice as a percussionist and helps to preserve this knowledge in future performances. In my own artistic work, lsl.lpsr has become a powerful instrument, whether for completely electronic perfor-mance or in combination with acoustic instruments. Espe-cially the latter provides surprising results on stage: as an
acoustic improviser responds naturally to his environment, using his sound as input for lsl.lpsr creates an interesting feedback cycle. For example in the improvising collective ‘Worp’ I perform with lsl.lpsr on virtual instruments and samplers, but I also manipulate the sound of the double bass player, the tuba player, the chant of the instrumental-ists and/or dancers and my own percussion playing. In a collaboration with percussionist Nueny Herreno Villa, I used Colombian musical patterns as presets in lsl.lpsr for manipulating sound of the live performance of those pat-terns on traditional Colombian percussion instruments. Lsl.lpsr has also been used to create electronic tracks for the exhibition ‘Let Yourself Fall’ix, performing on virtual instruments and manipulating spoken texts.
6. REFERENCES [1] G. Lelong, “Entretien avec Philippe Hurel,” in Les
cahiers de l’Ircam - Compositeurs d’aujourd’hui: Philippe Hurel, G. Lelong, Ed. Paris: Editions Ircam - Centre Georges-Pompidou, 1994, p. 93.
[2] S. D. Sorden, “The cognitive theory of multimedia learning,” in Handbook of Educational Theories, 2012, pp. 1–31.
[3] R. E. Mayer and R. Moreno, “Nine Ways to Reduce Cognitive Load in Multimedia Learning,” Educ. Psychol., vol. 38, no. 1, pp. 43–52, 2003.
[4] T. De Cock, V. Caers, and K. Van Den Buys, “An Examination of Philippe Hurel’s ‘Loops II,’” Percussive Notes, vol. 3, no. May, pp. 44–48, 2015.
[5] V. Caers, “Het loops-proces in het werk van Philippe Hurel,” Adem, vol. 4, no. Oktober, pp. 176–187, 2012.
[6] S. Weytjens, M. Delaere, and L. Van Hove, Tempo en tijd in de hedendaagse muziek, First edit. Leuven: Acco, 2007.
[7] S.-L. Tan, P. Pfordresher, and R. Harré, Psychology of Music: from sound to significance. Routledge, 2010. (especially chapter six on perception of musical time)
i ‘Loops I’ for flute solo, ‘Loops II’ for vibraphone solo, ‘Loops III’ for flute duo, ‘Loops IV’ for marimba solo, ‘Loops V’ for carillon. ii Limiting at 16 beats is related to the hardware used for performing. Theoretically the system can handle any number of beats. e iii Cf. tempo indications in musical scores iv Speed lists are chance, linear, exponential or Fibonacci v Metric modulations relate two tempi by equation of two independent rhythms, e.g. one sixteenth-triplet note equals a quarter in the next measure. Elliot Carter among others is especially known for using them.
vi The early tape works ‘Come Out’ and ‘It’s gonna rain’ up to ‘Drum-ming’ specifically explore this process vii As for example clearly present in ‘Clapping Music’ viii A rhythmical operation which is often encountered in non-occidental music, but is also particularly present in the music by Philip Glass ix See http://www.vincentcaers.be/projects
Figure 5: lsl.lpsr full patch. The top window shows the GUI of the sequencer, with pattern and alter sections. The bottom left window contains the main patch. The other two windows present the MIDI-router (left) and UDP-router (middle).
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