Expressive Articulation for Synthetic Music Performances
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Proceedings of the 2010 Conference on New Interfaces for Musical Expression (NIME 2010), Sydney, Australia Expressive Articulation for Synthetic Music Performances Tilo Hahnel¨ and Axel Berndt Department of Simulation and Graphics Otto-von-Guericke University, Magdeburg, Germany ftilo, [email protected] ABSTRACT 2. WHAT IS ARTICULATION? As one of the main expressive feature in music, articulation To trace the meaning of articulation it is ¯rst necessary to a®ects a wide range of tone attributes. Based on experimen- be aware of the di®erence between the notation of music tal recordings we analyzed human articulation in the late and its actual performance. Throughout this article the Baroque style. The results are useful for both the under- terms `note' and `tone' are strictly distinguished. A note is standing of historically informed performance practices and a symbol of a musical event. Its attributes indicate pitch, further progress in synthetic performance generation. This length, loudness, onset and timbre (instrumentation). A paper reports of our ¯ndings and the implementation in a tone, by contrast, is the actual physical event in a perfor- performance system. Because of its flexibility and univer- mance. Its attributes are pitch, duration and so forth that sality the system allows more than Baroque articulation. all correspond to the referring indications of the note. Ex- pression in music performance touches deviations from tone attributes and note indications. Both timing and dynam- Keywords ics shape musical structure by influencing tone onsets and Expressive Performance, Articulation, Historically Informed loudness values, respectively. Articulation as the forming Performance of the single tone adds further deviations (e.g., an accent on a crescendo). This concerns all tone features, which are loudness, pitch, duration, envelope, and also timbre. The 1. INTRODUCTION following description briefly introduces the parameter space articulation is involved in. Humans achieve expression in music performances by sev- eral features. Whatever is additionally named by di®erent Envelope: A tone can consist of the four parts attack, de- authors[12, 15, 5], all of them conform to three expressive cay, sustain and release. Every part can show di®erent features, which are timing, dynamics (loudness) and artic- proportions or even be absent. On the whole they de- ulation [10]. scribe the loudness progression over a single tone. Today's performance systems established articulation as tone duration [15], sometimes reduced to the span between Duration: It is the time from tone-onset to its o®set, either legato and staccato [7] or non-legato [13]. In this respect proportional to the inter onset interval (IOI) or in expressive articulation was measured [8, 14] and also imple- absolute time. mented into expressive performance rule systems [4]. Duration is indeed the most striking feature of articu- Loudness Deviations: Independently from the dynamic lation but is not its only one. Articulation describes the shape of a musical section, certain articulations influ- forming of a tone in all its facets. This also includes loud- ence loudness. ness, timbre, intonation, and envelope characteristics. This paper aims at three major tasks concerning expres- Timbre Deviations: Some articulation instructions par- sive articulation: First, articulation is supposed to influence ticularly refer to playing techniques (pizzicato, ham- duration, but all remaining tone features like loudness, tim- mered bow strokes). They a®ect timbre changes that bre, intonation, and envelope characteristics as well. Sec- are neither exclusively caused by loudness changes nor tion 2 introduces the whole range of these aspects. Based depend on instrumentation. on the ¯rst task, Section 3 shows our method demonstrating that di®erent articulations change these tone features. The Intonation Deviations: Similar to loudness and timbre, analysis exempli¯es Baroque articulation. Consequently, di®erent articulations may influence intonation [9]. Section 4 describes the implementation of articulation fea- Articulation can a®ect one or more of these tone features. tures including the possibility to freely de¯ne further artic- The following Section shows the analysis of envelope, tone ulation styles. A conclusion follows in Section 5. duration, and loudness deviations. 3. MEASURING ARTICULATION Permission to make digital or hard copies of all or part of this work for The meaning of articulations changed with time and place. personal or classroom use is granted without fee provided that copies are We therefore considered a stylistic homogeneity. In addi- not made or distributed for profit or commercial advantage and that copies tion, we wanted to choose key articulations for testing. The bear this notice and the full citation on the first page. To copy otherwise, to focus on German late Baroque/early Classic music ful¯lled republish, to post on servers or to redistribute to lists, requires prior specific both conditions; it reduced the range of interpretation and, permission and/or a fee. NIME2010, June 15-18, 2010, Sydney, Australia. on the other hand, supports articulations that are both rea- Copyright 2010 Copyright remains with the author(s). sonable and still valid today [1, 18]. 277 Proceedings of the 2010 Conference on New Interfaces for Musical Expression (NIME 2010), Sydney, Australia articulation max percentile o®set percentile a: 25 50 75 25 50 75 tenuto .363 .661 .780 .799 .893 .963 neutral .339 .469 .586 .692 .771 .876 b: bow vibrato .413 .495 .571 .693 .780 .812 portato 71 95 124 .533 .727 .769 c: tenuto * .532 .567 .744 staccato 73 87 101 160 173 225 d: neutral .466 .523 .624 staccatissimo 60 80 102 143 161 189 e: staccato* Table 1: Loudness distributions show time propor- f: staccatissimo tions to IOI, except italic letters that are ms values. g: bow vibrato* instrument. Regarding the directional characteristics of in- struments, this would have a®ected the recorded loudness h: portato values too much. Being aware that recorded decibel values depend on all recording conditions, we ran a dynamic range test with the same setting. So all decibel values addition- Figure 1: Exercises from Mozart: a(original) and ally were analyzed proportionally to the piano { forte range. b(experimental); Reichardt: d-h; *: additional. Tone onsets were extracted automatically by using the Sonic Visualiser2 and onset detection algorithms based on energy changes in frequency bands as well as power fluctuations 3.1 Methodology described by Duxbury et. al [6]. Missing and mismatched Figure 1 shows all articulations that were analyzed. They onsets were manually revised, for instance, if no or more are described as follows [1, 17, 18, 19]: than one onset were found on a single tone. Recordings were excluded, if musicians misinterpreted the annotations tenuto: Tones are to play as long as possible but clearly or were not able to perform them (the bow-vibrato is a par- separated from each other. ticular string annotation, so brass or woodwind instruments were not recorded). neutral: If notes are without any annotation it is to decide In the Reichardt exercises (see Figure 1c{h) all tones that how to articulate them. This depends on the respec- belonged to the same articulation were averaged for every tive common practice. The analysis refers to a promi- recorded instrument (see Figure 2). Envelope di®erences, nent example in Baroque music: Eighths (quavers) in release phase and reverberation impeded a de¯nite o®set the accompaniment are played short [17, 19]. detection. To indicate o®sets we decided to label an o®set marker where the loudness falls below 66 percent of the par- staccato/staccatissimo: It means very short/ as short as ticular loudness range of the particular mean articulation. possible. There the loudness decreased intensely but the signal was obviously not disrupted by reverberation. Figure 2 shows 1 bow vibrato: All notes under a slur are played by a con- the o®set markers for all averaged articulations that were tinuous increasing and decreasing bow pressure but played by one musician with one string instrument. Even without any stopping of the bow stroke. if the o®set marker and the real o®set point di®ered, most articulations could be distinguished by the o®set markers. portato: 1 All notes under a slur are played with one bow In addition to onset and o®set markers, we inserted max- stroke but clearly separated by stopping the bow. imum markers where the maximum loudness was reached. The combined onset, maximum and o®set markers allowed Because most standard Baroque articulation instructions a clear distinction of all tested articulations. emphasize duration, two special articulations with an em- phasis on (string) playing technique were added (Figure 1g 3.2 Results and h). The results taken from the experimental recordings con- We recorded ten professional musicians playing Baroque cern duration, loudness and envelope characteristics. In all and modern instruments; altogether we recorded 14 di®er- tests no systematic di®erences were found between mod- ent instruments, including strings, brass and woodwinds. ern and Baroque instruments or between string, brass and The exercises followed eighteenth century articulation prac- woodwinds. Admittedly, modern instruments showed an tises that had been taken from two major treatises on vio- increased maximum loudness value but no di®erences re- lin playing: Johann Friedrich Reichardt [19], i.e., Reichardt garding the piano{forte range. exercise, and Leopold Mozart [17], i.e. Mozart exercise, as shown in Figure 1. Duration Two AKG 1000 microphones were placed two meters in front of the instrument. A larger distance would have en- Table 1 summarizes the results of the Reichardt exercise. tailed less loudness di®erences and increased recorded re- Every position of the maximum and o®set markers was an- verberation. On the contrary, a closer position would carry alyzed in absolute time (absolute condition) and propor- the risk that body movements influence the position of the tionally to the IOI (proportional condition).