The following represents the text of a presentation, which included a performance of the composition discussed, given at the Sonic Art Research Unit Symposium at Oxford Brookes University.

Breath across autumnal ground Sohrab Uduman

For harpsichord and real-time computer transformation

Overview

The characteristics of the harpsichord presented the starting point for this piece. In trying to find a contemporary context and compositional approach to the business of working with an instrument associated with a particular epoch, which carries an established repertoire and tradition of performance, the relationship between the instrument itself and its past musical material provides a useful perspective for viewing possibilities for forming musical material. This can be understood by considering the relatively fixed nature of the sound itself: essentially a plucked, attack based, sound with a more or less perceptible rapid rate of decay; one where point to point intensity remains fixed and can only be altered and hence shaped by modifying the weight of a structure. At first sight it appears that some of the principal structural and expressive gambits in contemporary compositional practice, involving modifying and modulating timbre, dynamics and articulation, are only available, if at all, to limited degrees. When one considers the instrument’s past repertoire, however, the articulation of musical structural elements, whether they be harmonic or melodic, can be seen in certain instances to be undertaken by the texture of the music customised to the instrument’s inherent nature, for example in terms of layout, registration, chord articulation, species of ornamentation. One could even say that the music constructs the instrument, brings the instrument into being, to the same degree that the instrument serves as a means of articulating musical ideas. In the present piece the two resources, harpsichord and live electronics, function rather in the manner of a single instrument in their use of consistent textures, or textures which have a particular character or trajectory, and associated means of processing.

There are two broad aspects to the form of Breath across autumnal ground; musical and poetic. In musical terms there are two underlying ideas: firstly the notion of going over the same ground, rather like a ground bass or passacaglia; secondly, the accumulation and stripping away of material covering and revealing facets of the basic material. In the latter case no basic ‘primordial’ piece of material is revealed in its entirety; instead the process strips the material of substance without exposing the complete underlying structure. From the poetic viewpoint the title of the piece alludes to this sense of accumulation, motion and, in a sense, fragmentation associated with seasonal changes in colour, content and texture in the natural world. This is heard in the changes of textural density and forms of articulation, in both instrumental and computer processed materials, corresponding in some measure to a means of varying intensity. The idea of wind and breath is also expressed in the piece’s use of certain types of resonating and sustained sounds, generated by processing the instrument’s material.

Musical material

The musical fabric unfolds as the basic harmonic and rhythmic structures of the piece are revisited from several viewpoints. A line or structure initially presented in a particular setting is subjected to, on the one hand, a process of enrichment of textural detail, vertically and horizontally and on the other to a process of reduction, where the features are condensed to their basic elements. An equivalent process can be heard in the relationship between the instrument and computer transformation as the temporal balance between the instrument’s material and its transformation shifts from relative separation of gestures, utterances, of the two media to the near simultaneous processing of material, where the two elements fuse, and finally to the enveloping of the harpsichord’s gestures by its processed resonating material.

The form of the piece is based on the combining of three structures previously outlined, corresponding to the presentation of a model, its enrichment and reduction. Each structure has a particular set of characteristics.

• Type A – linear, texturally consistent material, single mode of articulation, legato; phrases separated according to harmonic and duration structures; constant regular pulse; middle registral placement

• Type B – linear-vertical gestures, changing evolving texture, mixed and evolving mode of articulation; structures fragmented then coalesced; irregular pulse changing to regular sustained texture; middle to low registral placement giving way to mid to high

• Type C – Single phrase type, consistent form of articulation; unpulsed, fragmentary rhythm; low-high registral placement

The shape of the piece, where an initially consistent texture gives way to breaks and interruptions in its course, arises from the way these structures are placed. Types A and B are intercut; the consistent, unvarying legato melodic material of the former giving way to predominantly vertical, evolving material (trills, staccato chords changing to legato then staccatissimo material). Type C , juxtaposed against these two ideas at the end as a kind of extended coda, refers in passing to the placement of the two other types; predominantly vertical material alternates with displaced melodic fragments. It should be said that although the material for the work is generated according to different sets of characteristics accorded its content the intention behind its shape is to create a form which is continuous and evolves from one state to another, rather than presenting a sectional block-like form.

Computer transformation

Three principal treatments are employed, in real-time, in various configurations.

• Granulation
• Harmonisers
• Filtering

In addition to these there are secondary processing configurations such as reverberation, delay, compression, input-output filtering which exist for practical reasons and also serve to enhance the output of the principal processes.

The musical functions of the processes are: to create sustaining and resonating sounds from the harpsichord’s material; to add layers, create the impression of other parts/polyphony; modify the harpsichord’s timbre. Of the three the first two are the most significant in terms of use and material generated whilst the third is employed to a lesser degree, although mainly in the final sections of the piece.

Granulation (based on Granular Synthesis v2.5 by N Sakonda) in this instance involves the capturing and buffering of the harpsichord’s material for timestretching and granulation. Slow buffer reading speeds and large grain sizes lead to sustained texture whilst relatively fast read rates and smaller grain sizes produces comparatively fragmented material.

Harmonisers (using IRCAM Jimmies and Bennies) serve to thicken textures (mainly the output from granulation) and expand the harpsichord’s material harmonically – both vertically and linearly – by varying internal delay and feedback rates. In addition, some degree of timbral alteration is effected by using relatively small window sizes often in combination with high feedback or short delay rates.

Two discrete filtering configurations are used; six multifunction filters in parallel and four comb filters in two pairs. Interpolation between parameters (cf, q, gain for multifilters, frequency and intensity for combs) allows the creation of voice-like qualities in sustained textures as well as metallic, percussive colouration (the latter can be heard particularly in the final section of the piece).

Each type of musical structure is associated with a particular configuration or set of configurations.

Type A – recording and retaining (about a 3 sec. sample) sound into a closed buffer for granulation/timestretch using slow read rate of -0.06 and relatively large grain durations (140 to 200 ms), thickened by three harmonisers using low internal delays and moderate to high feedback levels (^+/-33 – ^+/-85%), the higher values used to enhance lower notes in the output. It should be noted here that the use of a negative reading direction (the buffer reading is done by a function/oscillator) for the granulation reverses the envelope of the buffered sound’s components whilst the harmonisers’ settings are based on the harmonic material contained in the harpsichord’s gestures in the final section of the piece (based on type C material).

Type B – comparatively fast perceptible granulation with respect to type A - rapid buffer read rate of around 8 into an open buffer (the buffer is constantly renewed at a rate depending on the buffer size), small grain size (50 ms) - changing to a larger grain duration and slower read rate (0.1) to create overlaps, larger grain delta value (around 50%), which are then fed into harmonisers for delay and thickening. Here, the use of feedback and delay works in conjunction with a buffer length of around 1 sec. to create the effect of an additional harmonically linked structure or part changing at a slower rate; the open buffer (renewed every second or so) ensures that there is minimal distance between the harpsichord’s antecedent input material and the cascade of answers output by the configuration.

Type C – has two elements working in overlap and alternation. In the first the dry sound together with its granulated form is first thickened by the harmonisers, then sent through filters whose parameters constantly vary. Here, the granulated harmonic material is thrown through the evolving colouration of the filters. In the second element a mix of direct and reverberated sound is fed through comb filters; the melodic shards previously mentioned are coloured by a fixed configuration, but one where the output depends on the register, the timbre (depending on high or low register) of the input material.

Observations

To a large extent the processing, in terms of its musical intent, is directed to the extension of the harpsichord’s sound, the stretching and extension of the sound itself as well as enhancing and enriching harmony. Other factors particular to the harpsichord which give the processing its particular feature, its colouration and hence its function in combination with the harpsichord as an instrument, are:

- use of the qualities of natural resonances from the strings and soundboard, perceptible to the performer but not usually to a listener positioned some distance from the instrument

• the nature of the harpsichord’s attack and release of sounds – contact sound from plectra as well the return of the keys and jacks
• the complex sounds created by the above two when arpeggiating, when attacking and releasing chords

SU

(Music, University of Keele)

7 June 2007