Helena Daffern

Four-part choral synthesis system for investigating intonation in a cappella choral singing

Abstract Accurate tuning is an important aspect of singing in harmony in the context of a choir or vocal ensemble. Tuning and ‘pitch drift’ are concerning factors in performance for even the most accomplished professional choirs when singing a cappella (unaccompanied). In less experienced choirs tuning often lacks precision, typically because individual singers have not developed appropriate listening skills. In order to investigate accuracy of tuning in ensemble singing situations, a chorally appropriate reference is required against which frequency measurements can be made. Since most basic choral singing involves chords in four parts, a four-part reference template is used in which the fundamental frequencies of the notes in each chord can be accurately set. This template can now be used in experiments where three of the reference parts are tuned in any musical temperament (tuning system), in this case equal and just temperaments, and played over headphones to a singer to allow her/his tuning strategy to be investigated. This paper describes a practical implementation of a four-part choral synthesis system in Pure Data (Pd) and its use in an investigation of tuning of notes by individual singers using an exercise originally written to explore pitch drift in a cappella choral singing.

Using electrolaryngography and electroglottography to assess the singing voice: a systematic review

Electrolaryngography (Lx) and electroglottography (EGG) are noninvasive methods used to assess human vocal fold vibration and investigate speech and singing. This paper provides a systematic review of evidence-based studies using Lx/EGG in the analysis of the singing voice, identifying and critically appraising the thematic content and the research methodologies of the relevant investigations. Lx/EGG represents a powerful tool for the analysis of the singing voice in medical settings, and in support of research and teaching. Current research in this area is paving the way toward a better comprehension of singing performance.

Voice source comparison between modern singers of early music and opera.

Abstract An experiment was conducted comparing two subject groups, each comprised of eight professional singers specializing in a genre of classical music: early music or grand opera. Electroglottography was used to consider vocal characteristics idiomatic to each genre. Whilst there are clear differences in contact quotient between subjects, particularly when relationships between fundamental frequency (f0) and contact quotient (Qx) are considered, there is no apparent link between contact quotient behaviour and performance specialism based on the results of this sample.

A new method of onset and offset detection in ensemble singing

Abstract This paper presents a novel method combining electrolaryngography and acoustic analysis to detect the onset and offset of phonation as well as the beginning and ending of notes within a sung legato phrase, through the application of a peak-picking algorithm, TIMEX. The evaluation of the method applied to a set of singing duo recordings shows an overall performance of 78% within a tolerance window of 50 ms compared with manual annotations performed by three experts. Results seem very promising in light of the state-of-the-art techniques presented at MIREX in 2016 yielding an overall performance of around 60%. The new method was applied to a pilot study with two duets to analyse synchronization between singers during ensemble performances. Results from this investigation demonstrate bidirectional temporal adaptations between performers, and suggest that the precision and consistency of synchronization, and the tendency to precede or lag a co-performer might be affected by visual contact between singers and leader–follower relationships. The outcomes of this paper promise to be beneficial for future investigations of synchronization in singing ensembles.

Synchronization in Singing Duo Performances: The Roles of Visual Contact and Leadership Instruction

Interpersonal synchronization between musicians during ensemble performances is characterized by continuous micro-timing adjustments due to intentional and unintentional factors supporting expressive interpretations, or caused by noise during the cognitive-motor process. Whether visual contact between musicians and the instruction to act as leader or follower affect synchronization in ensembles remains mostly unclear. This study investigates the role of visual cues and leader-follower relationships in singing performances. Twelve vocal duos took part in the study, singing a two-part piece, which was composed for the study and was mostly homophonic in structure. Four conditions were applied in a randomized order: with and without visual contact, and with a designated leader or follower. The piece was repeated four times in each condition, and the condition presented three times, for a total of 12 performances of the piece in each condition. Data were acquired using electrolaryngograph electrodes and head mounted microphones to track the fundamental frequency estimates of the individual singers. Results show that the presence and absence of visual contact had a significant effect on the precision and consistency of synchronization during singing duo performances. Precision and consistency were better in the presence of visual contact between singers than without, and these effects were associated with the beginning of phonation of the first note of the piece. The presence/absence of visual contact also had an effect on the tendency to lead or lag a co-performer associated with the onset of the first note; the extent of leading was greater when visual contact was absent. The instruction to act as leader or follower did not affect precision or consistency of synchronization, nor did it relate to the observed tendency to precede or lag a co-performer. The results contribute to the tailoring of rehearsal strategies, as singers and directors can be better informed of the factors influencing synchronization and focus on specific areas of difficulty in certain performance conditions, such as first note onsets when performers are not able to see each other.

A Longitudinal Study Investigating Synchronization in a Singing Quintet

Research suggests that synchronization between musicians during ensemble performances can be affected by the rhythmic or tonal complexity of the piece being performed and by group roles such as leader-follower relationships. Since previous studies have mostly been conducted within single performance sessions, developmental aspects of interpersonal synchronization in ensembles remain underinvestigated. This longitudinal study followed a newly formed singing ensemble from initial rehearsals to the performance stage in order to investigate the evolution of synchronization between advanced singing students during a university term of study in relation to the musical content of the piece and leader-follower relationships. An advanced postgraduate singing quintet was recorded using head-worn microphones and laryngograph electrodes to allow fundamental frequency evaluation of the individual voices. The quintet, formed to complete a 1-year Masters programme in ensemble singing, rehearsed two pieces composed for the study, during five rehearsals over 3 months. Singers practised the same pieces in a randomized order across rehearsals and performed three repetitions of the same pieces before and after each rehearsal, resulting in six recordings per piece/rehearsal. Audio and laryngograph data of the repeated performances were collected, and synchronization was measured by extracting note times from the fundamental frequency values. The asynchronies of the two pieces before and after rehearsals were calculated and compared both within rehearsals (pre and post) and between rehearsals (rehearsals 1-5). Results demonstrate an increase in the precision of synchronization over the course of study, depending on the piece being rehearsed, and a more variable synchronization for the more rhythmically complex piece. Results also show changes in the distribution of the tendency to precede all co-performers across rehearsals, which became equally distributed among the musicians during the last rehearsal. The results reported here could have important implications for the tailoring of rehearsal strategies that could improve interpersonal synchronization between musicians during ensemble performances.

Determining the Relevant Criteria for Three-dimensional Vocal Tract Characterization

OBJECTIVE Soprano singers face a number of specific challenges when singing vowels at high frequencies, due to the wide spacing of harmonics in the voice source. The varied and complex techniques used to overcome these are still not fully understood. Magnetic resonance imaging (MRI) has become increasingly popular in recent years for singing voice analysis. This study proposes a new protocol using three-dimensional MRI to investigate the articulatory parameters relevant to resonance tuning, a technique whereby singers alter their vocal tract to shift its resonances nearer to a voice source harmonic, increasing the amplitude of the sound produced. METHODS The protocol was tested with a single soprano opera singer. Drawing on previous MRI studies, articulatory measurements from three-dimensional MRI images were compared to vocal tract resonances measured directly using broadband noise excitation. The suitability of the protocol was assessed using statistical analysis. RESULTS No clear linear relationships were apparent between articulatory characteristics and vocal tract resonances. The results were highly vowel dependent, showing different patterns of resonance tuning and interactions between variables. This potentially indicates a complex interaction between the vocal tract and sung vowels in soprano voices, meriting further investigation. CONCLUSIONS The effective interpretation of MRI data is essential for a deeper understanding of soprano voice production and, in particular, the phenomenon of resonance tuning. This paper presents a new protocol that contributes toward this aim, and the results suggest that a more vowel-specific approach is necessary in the wider investigation of resonance tuning in female voices.

The Perception of Formant Tuning in Soprano Voices

INTRODUCTION At the upper end of the soprano range, singers adjust their vocal tract to bring one or more of its resonances (Rn) toward a source harmonic, increasing the amplitude of the sound; this process is known as resonance tuning. This study investigated the perception of (R1) and (R2) tuning, key strategies observed in classically trained soprano voices, which were expected to be preferred by listeners. Furthermore, different vowels were compared, whereas previous investigations have usually focused on a single vowel. METHODS Listeners compared three synthetic vowel sounds, at four fundamental frequencies (f0), to which four tuning strategies were applied: (A) no tuning, (B) R1 tuned to f0, (C) R2 tuned to 2f0, and (D) both R1 and R2 tuned. Participants compared preference and naturalness for these strategies and were asked to identify each vowel. RESULTS The preference and naturalness results were similar for /ɑ/, with no clear pattern observed for vowel identification. The results for /u/ showed no clear difference for preference, and only slight separation for naturalness, with poor vowel identification. The results for /i/ were striking, with strategies including R2 tuning both preferred and considered more natural than those without. However, strategies without R2 tuning were correctly identified more often. CONCLUSIONS The results indicate that perception of different tuning strategies depends on the vowel and perceptual quality investigated, and the relationship between the formants and (f0). In some cases, formant tuning was beneficial at lower f0s than expected, based on previous resonance tuning studies.

A Longitudinal Study of Intonation in an a cappella Singing Quintet

OBJECTIVE The skill to control pitch accurately is an important feature of performance in singing ensembles as it boosts musical excellence. Previous studies analyzing single performance sessions provide inconclusive and contrasting results on whether singers in ensembles tend to use a tuning system which deviates from equal temperament for their intonation. The present study observes the evolution of intonation in a newly formed student singing quintet during their first term of study. METHODS/DESIGN A semiprofessional singing quintet was recorded using head-worn microphones and electrolaryngograph electrodes to allow fundamental frequency (fo) evaluation of the individual voices. In addition, a camcorder was used to record verbal interactions between singers. The ensemble rehearsed a homophonic piece arranged for the study during five rehearsal sessions over four months. Singers practiced the piece for 10 minutes in each rehearsal, and performed three repetitions of the same pieces pre-rehearsal and post-rehearsal. Audio and electrolaryngograph data of the repeated performances, and video recordings of the rehearsals were analyzed. Aspects of intonation were then measured by extracting the fo values from the electrolaryngograph and acoustic signal, and compared within rehearsals (pre and post) and between rehearsals (rehearsals 1 to 5), and across repetitions (take 1 to 3). Time-stamped transcriptions of rehearsal discussions were used to identify verbal interactions related to tuning, the tuning strategies adopted, and their location (bar or chord) within the piece. RESULTS/DISCUSSION Tuning of each singer was closer to equal temperament than just intonation, but the size of major thirds was slightly closer to just intonation, and minor thirds closer to equal temperament. These findings were consistent within and between rehearsals, and across repetitions. Tuning was highlighted as an important feature of rehearsal during the study term, and a range of strategies were adopted to solve tuning related issues. This study provides a novel holistic assessment of tuning strategies within a singing ensemble, furthering understanding of performance practices as well as revealing the complex approach needed for future research in this area. These findings are particularly important for directors and singers to tailor rehearsal strategies that address tuning in singing ensembles, showing that approaches need to be context driven rather than based on theoretical ideal.

Diphthong Synthesis Using the Dynamic 3D Digital Waveguide Mesh

Articulatory speech synthesis has the potential to offer more natural sounding synthetic speech than established concatenative or parametric synthesis methods. Time-domain acoustic models are particularly suited to the dynamic nature of the speech signal, and recent work has demonstrated the potential of dynamic vocal tract models that accurately reproduce the vocal tract geometry. This paper presents a dynamic 3D digital waveguide mesh (DWM) vocal tract model, capable of movement to produce diphthongs. The technique is compared to existing dynamic 2D and static 3D DWM models, for both monophthongs and diphthongs. The results indicate that the proposed model provides improved formant accuracy over existing DWM vocal tract models. Furthermore, the computational requirements of the proposed method are significantly lower than those of comparable dynamic simulation techniques. This paper represents another step toward a fully functional articulatory vocal tract model which will lead to more natural speech synthesis systems for use across society.