Vibrato Rate Research Articles

An Analysis of Double Bass Vibrato

The purpose of this study was to investigate the rates, widths, and pitches of university double bass players’ vibrato in relation to pitch height, fingers used, and tempo. Forty ( N = 40) undergraduate and graduate double bass players performed excerpts in first, fourth, and thumb positions. The overall mean vibrato rate and width was 5.17 Hz and 19 cents. Analyses indicated that university double bassists employed faster vibrato rates and increased width as they performed in progressively higher registers. The third and fourth fingers vibrated the fastest, but the second finger produced the largest width. Musical examples played with a fast tempo were both faster and wider (5.35 Hz, 20 cents) than musical examples played with a slow tempo (4.94 Hz, 19 cents). Participants vibrated almost equally above and below the in-tune pitch—overall mean pitches of vibrated and non-vibrated tones varied by 1 cent. Music educators may use these results to create more consistent descriptions of double bass vibrato and, potentially, more efficient methods for teaching vibrato.

단음을 기반으로 한 해금 농현의 특성 분석에 대한 연구

Vibrato, called nonghyeon or nongeum , is one of the typical performance
 techniques frequently used in gugak (Korean traditional music). There have
 been studies that analyzed the characteristics of vibrato of vocal and wind
 instruments in the field of gugak . However, there are not many studies that
 objectively analyzed the characteristics of vibrato of haegeum, one of the
 representative Korean traditional string instruments. This study examines the
 characteristics of haegeum vibrato, using strong, medium, and soft monotones
 of haegeum from the digital sound sources provided by the National Gugak
 Center. It analyzes 42 haegeum monotones specifically in terms of intonation,
 vibrato rate, and vibrato extent.
 As a result, the vibrato speed in haegeum is around 4 Hz (four times per
 second), which is generally lower than that in Western music. The vibrato
 extent ranges from 60 cents to 153 cents on average per note, which covers a
 somewhat larger range compared to that in Western music. In addition, there
 are some discussions regarding the tendency for the vibrato rate to increase,
 which appeared at the end of some vibratos, and the results of the vibrato
 extent according to strong, medium, and soft playing in monotones.
 This study is significant in that it has provided basic data on the
 characteristics of the haegeum vibrato, but also has a limitation of analyzing
 only monotones played by a single performer. It is hoped that future research
 will be conducted to analyze the characteristics of haegeum vibrato on various
 pieces performed by multiple performers.

Understanding the coherence properties of musical vibrato signals

In the field of optics, coherence theory is used to characterize the relative correlation of optical fields at different points in space and time. While this framework has found fewer applications in acoustics outside of an imaging context, recent work has explored the possibility of characterizing rooms and other acoustical systems based on the coherence properties of naturally occurring reverberant sounds. Additionally, the cross-correlation functions used in coherence theory also underly many auditory perceptual models which leverage interaural correlations to estimate interaural time differences (ITD) used in sound localization. In these contexts, musical vibrato constitutes an important type of partially coherent signal. The quasiperiodic frequency, and often amplitude, modulation inherent to natural vibrato serves to reduce the coherence time of the sound, while being defined by a small set of relatively constant control parameters. This presentation will describe the relative impact of vibrato performance parameters, including vibrato rate and depth, on the coherence properties of the signal for various instruments. Analysis of recorded instrument samples will be compared predictions from a sinusoidal synthesis model for both the dry and reverberant cases. Finally, the potential for characterizing other musical systems, such as instruments, using coherence theory will be explored.

Experienced Listeners’ Perception of Timbre Dissimilarity Within and Between Voice Categories

The terms "soprano" and "mezzo-soprano" are frequently used by vocal pedagogues to describe a main category of singing timbre categorization, while the terms "lyric" and "dramatic" are often used to describe sub-categories of "soprano" and "mezzo-soprano". A handful of studies have reported on the perceptual dissimilarity of main voice categories, but few, if any, have focused on within voice category perceptual distinctions such as dramatic and lyric vocal timbre. Using stimuli collected from cisgender female singers of varying voice categories and voice weights across the pitches C4, G4, and F5, this study sought (1) to visualize an experienced listener's perception of vocal timbre dissimilarity within and between voice categories using the statistical technique of multidimensional scaling (MDS), (2) to identify salient acoustic predictors of voice category and voice weight, and (3) to determine any dependencies on pitch for the perception of vocal timbre. For the pitches C4, G4, and F5, experienced listeners (N=18) rated the dissimilarity of pairs of sung vowels produced by classically trained singers classified as follows: six mezzo-sopranos (three lighter and three heavier) and six sopranos (three lighter and three heavier). The resulting dissimilarity data were analyzed using MDS. Backward linear regression was used to see if one or more of the following variables predicted MDS dimensions: spectral centroid from 0 to 5 kHz, spectral centroid from 0 to 2 kHz, spectral centroid from 2 to 5 kHz, frequency vibrato rate, and frequency vibrato extent. Listeners also completed a categorization task where they rated each individual stimulus on two dimensions: voice category and voice weight. Visual analysis of the MDS solutions appears to show that both voice category and voice weight emerged as dimensions at pitches C4 and G4. Discriminant analysis, on the other hand, statistically confirmed both these dimensions at G4, but only voice weight at C4. At pitch F5, only voice weight emerged as a dimension, both visually and statistically. Acoustic predictors of MDS dimensions were highly variable across pitches. At the pitch C4, no MDS dimension was predicted by the acoustic variables. At pitch G4, the dimension associated with voice weight was predicted by spectral centroid from 0 to 2 kHz. At pitch F5, the dimension associated with voice weight was predicted by spectral centroid from 2 to 5 kHz and frequency vibrato rate. In the categorization task, voice category and voice weight were highly correlated at the pitches C4, G4, and when all pitches were presented together, but weakly correlated at the pitch F5. While voice category and sub-category distinctions are commonly used by singing voice professionals to describe the overall timbre of voices, these distinctions may not be able to consistently predict the perceptual difference between any given pair of vocal stimuli, particularly across pitch. Nonetheless, these dimensions do emerge in some fashion when listeners are presented with paired vocal stimuli. On the other hand, when asked to rate stimuli according to the specific labels of mezzo-soprano/soprano and dramatic/lyric, experienced listeners have a very difficult time disentangling voice category from voice weight when presented with a single-note stimulus or even a 3-note stimulus consisting of the pitches C3, G4, and F5.

Assessing Acoustic Parameters in Early Music and Romantic Operatic Singing

Since the recent early music (EM) revival, a subset of singers have begun to specialize in a style of singing that is perceptually different from the more "mainstream" romantic operatic (RO) singing style. The aim of this study is to characterize EM with respect to RO singing in terms of its vibrato characteristics and the singer's formant cluster. This study presents a within-subject experimental design. Ten professional singers (5 F; 5M) versed in both EM and RO repertoire were enrolled in the study. Each singer recorded the first 10 bars of the famous Aria, "Amarilli Mia Bella" (Giulio Caccini, 1602) a cappella, in RO and EM styles, in random order. Three sustained notes were extracted from the acoustical recordings and were analyzed using the free user-friendly software Biovoice to extract five parameters: vibrato rate, vibrato extent, vibrato jitter (Jvib), vibrato shimmer, and quality ratio (QR), an estimation of the singer's formant power. Vibrato in EM singing was characterized by a higher rate, a smaller extent, and less regular cycle-cycle period duration (higher Jvib) compared to RO singing. As in previous studies, RO singing presented a more prominent singer's formant, as indicated by a smaller QR. Acoustical analysis of some vibrato characteristics and the Singer's Formant significantly differentiated EM from RO singing styles. Given the acoustical distinctions between EM and RO styles, future scientific and musicological studies should consider distinguishing between the two styles rather than using a singular term for and description of Western Classical singing.

Perception of vibrato rate by professional singing voice teachers

This study sought to investigate how voice clinicians perceive vibrato rate alterations when presented with controlled, synthesized singing voice samples which vary in vibrato rate and vibrato extent. Thirty-four professional voice teachers completed a twelve-item demographic survey and performed a visual sort and rate task (VSR). For the VSR task, each participant listened to twenty synthesized samples and sorted them from slowest vibrato rate to fastest vibrato rate. This task resulted in distance (i.e. individual perception of vibrato rate) and rank-difference measurements for each sample. Two generalized linear mixed effects models (GLMM) and one linear model (LM) were computed. Results for GLMM’s found significant associations between vibrato extent and vibrato rate and both individual perception of vibrato rate and rank-difference. Results for the LM found no significant relationships between demographic information and absolute total ranking error. From the results of this study, it seems that both vibrato extent and vibrato rate influence the perception of vibrato rate for professional voice teachers. Neither age nor teaching experience seemed to relate to the ability to discern vibrato rate accurately.

The Use of Vibrato in Belt and Legit Styles of Singing in Professional Female Musical-Theater Performers

Musical theater (MT) performers are required to sing in several different styles, requiring different registration (quality) and different use of vibrato. Many measures of vibrato in MT performers are made in laboratory settings, studying a limited set of pitches, intensities, and vowels, using amateur and not well-defined professional singers. It is unclear if these observations are observed in well-known professional MT singers, during live instrumentally accompanied legit and belt performances. Descriptive from a convenience sample. Five well-known MT performers' recordings of one legit and one belt performance were downloaded for analysis of vocal vibrato. The vocal part was extracted from the recording and each note demarcated with and without vibrato. The pitch track of each note was analyzed for average pitch, duration, the proportion of a note sung with vibrato, if present, and written to file. The pitch track (f0 and time stamps) was written to a separate file for further analysis. This analysis consisted of vibrato rate (Hz), vibrato extent (semitones), and cycle-to-cycle perturbation (jitter-local and shimmer-local). The most consistent finding was that the belt performances of the five singers had lesser proportion of notes sung with vibrato than their legit performances. The next consistent finding was that during belt performances, when vibrato was used, it was for a shorter duration within a note. There was a trend for the average rate of vibrato to be slower in the belt performances, but not to a substantial degree. There was no clear difference between legit and belt performances for vibrato extent or cycle-to-cycle perturbation. For these five performers, the strategy for the use of vibrato most often employed for differentiating the two singing styles was using less vibrato and when used to engage it for a shorter portion of a sung note. We believe this study offers reasonable ecological validity in how professional MT performers utilize vibrato to distinguish between belt and legit styles of singing. Vibrato rate and extent are subject to a number of factors which may not be in direct control of the singer. However, learning to sing with and without vibrato and the duration to which it is produced within a note may be a useful training strategy for students of MT.

Singing in different performance spaces: The effect of room acoustics on vibrato and pitch inaccuracy.

Previous literature suggests that musical performers may be influenced to some extent by the acoustic environment in which they sing or play. This study investigates the influence of room acoustics on singers' voice production, by analyzing consecutive sung performances of classically trained students in five different performance spaces. The analyzed voice parameters were vibrato rate, extent, and pitch inaccuracy. Nine classically trained student-singers performed the same aria unaccompanied on a variable starting pitch that was consistent between spaces. Variance in vibrato rate and pitch inaccuracy was primarily explained by individual differences between singers. Conversely, the variance attributable to the rooms for the parameter of vibrato extent was larger compared to the variance attributable to the performers. Vibrato extent tended to increase with room clarity (C80) and was inversely associated with early decay time (EDT). Additionally, pitch inaccuracy showed a significant negative association with room support (STv). Singers seem to adjust their vocal production when performing in different acoustic environments. Likewise, the degree to which a singer can hear themself on stage may influence pitch accuracy.

The effect of acoustic environments on singers’ vocal behaviors and mental effort

Singers perform in various acoustic environments; however, how the environments affect their mental effort is poorly understood. This study virtually simulated acoustic environments to examine the effect of reverberation time on singers’ vocal behaviors and mental effort. Participants were five vocally healthy singers who completed a minimum of undergraduate-level training. For the virtual environments, the voice signal was digitally processed by adding reverberation using a real-time effect processor of the digital mixer. The processed sound was played back to the participant using open headphones. The average T30 was 1.13 s in Low T30 condition, 1.39 s in Medium T30 condition, and 1.90 s in High T30 condition. Participants sang the American national anthem and rated their perceived level of overall effort, mental effort, physical effort, frustration, and performance using a modified NASA-TLX scale for each acoustic condition. Pupillometry was also used to measure the mental effort during each task. Their voice recordings were acoustically analyzed for intensity, singing-power ratio, alpha ratio, pitch accuracy, and vibrato rate and extent. The presentation will discuss: (1) individual differences in the participants’ response to the reverberation time and (2) the degree of agreement between the subjective rating and physical measurement of mental effort.

Objective Measures of Two Musical Interpretations of an Excerpt From Berlioz's “La mort d'Ophélie”

This study aimed to determine objective production differences relative to two emotional interpretations in performing an excerpt from a classical art song. The null hypothesis was proposed. The first author recorded an excerpt from an art song. The excerpt was sung with two contrasting musical interpretations: an "empathetic legato" approach, and a "sarcastic" approach characterized by emphatic attacks. Microphone, airflow, and electroglottography signals were digitized. The vowels were analyzed in terms of intensity, long term average spectra, fundamental frequency (fo), airflow vibrato rate and extent, vowel onset slope, intensity comparison of harmonic frequencies, and glottal measures based on electroglottograph waveforms. Four consonant tokens were analyzed relative to airflow, voice onset time, and production duration. The emphatic performance had faster vowel onset, increased glottal adduction, increased intensity of harmonics in 2-3 kHz, increased intensity in the fourth and fifth formants, inferred subglottal pressure increase, increased airflow for /f/, and greater aspiration airflow for /p, t/. Vibrato extents for intensity, fo, and airflow were wider in the emphatic approach. Findings revealed larger EGGW25 and peak-to-peak amplitude values of the electroglottography waveform, suggesting greater vocal fold contact area and longer glottal closure for the emphatic approach. Long-term average spectrum analyses of the entire production displayed minor variation across all formant frequencies, suggesting an insignificant change in vocal tract shaping between the two approaches. This single-case objective study emphasizes the reality of physiological, aerodynamic, and acoustic production differences in the interpretive and pedagogical aspects of art song performance.

Lyric or Dramatic - Vibrato Analysis for Voice Type Classification in Professional Opera Singers

Vibrato is one of the most frequently investigated parameters in singing. Most studies examine a very limited number of sound samples to answer specific questions. In the novel approach of our interdisciplinary vibrato project, a comprehensive database of 1723 sound samples was compiled, containing examples from 30 operas, one oratorio and 73 vocal exercises. Single tones undisturbed by orchestral sound were selected in the vocal registers soprano, tenor, baritone and bass according to a standardized classification system dividing voices into either a lyric or dramatic voice type. Various algorithms were implemented in a Matlab environment to automatically evaluate sound samples, with respect to vibrato extent and rate. An AM/FM demodulation scheme is presented with postprocessing required for automatic calculation of these two parameters. The vibrato extent was higher for the dramatic compared to the lyric voice type in soprano and tenor voices. In contrast, the extent of lyric baritones was significantly higher than for dramatic ones. Moreover, the vibrato rate was slightly lower for the dramatic voice type in all vocal registers. It turned out that the classification of bass voices into lyric and dramatic, unlike the other vocal registers, was not scientifically reproducible with our methods. Further vibrato results regarding aging, intra-individual and general stylistic development over time are presented and their possible relevance for vocal pedagogy are discussed.

Maintaining Professional Performance Viability With Age

Some classically trained singers demonstrate great performance longevity. These singers continue to produce a professionally viable voice that belies their age. This study was designed to assess selected acoustic characteristics of 10 currently performing classical singers from 2 recordings; one early, and one recent. The mean age at the early and recent recording was 39 and 64, respectively, with a mean of 25 years between recordings. Vibrato rate, extent, and consistency were calculated. The singers also completed a questionnaire to determine their strategies to maintain high-quality vocal production. From the early to recent recordings, overall, the participants demonstrated the expected decrease in vibrato rate, with little change in vibrato extent and consistency. The reported strategies included very individualized approaches regarding vocalizing regimens and maintenance of pitch accuracy. All agreed on the importance of increased self-awareness, openness to feedback, and dedicated preparation for upcoming performance. Our findings indicate that some singers are indeed ageless, but this attribute is not inherent; rather it requires diligent and devoted practice.

Effects of Historical Recording Technology on Vibrato in Modern-Day Opera Singers

Past literature indicates that vibrato measurements of singers objectively changed (i.e., vibrato rate decreased and vibrato extent increased) from 1900 to the present day; however, historical audio recording technology may distort acoustic measurements of the voice output signal, including vibrato. As such, the listener's perception of historical singing may be influenced by the limitations of historical technology. This study attempts to show how the wax cylinder phonograph system-the oldest form of mass-produced audio recording technology-alters the recorded voice output signal of modern-day singers and, thus, provides an objective lens through which to study the effect(s) of historical audio recording technology on vibrato measurements. Twenty professional Western opera singers sang a messa di voce on the vowel [a] and on the pitch C4 for male singers and C5 for female singers, three times into a flat-response omnidirectional microphone and onto an Edison Home Phonograph simultaneously. The middle 1-3 seconds (6-10 vibrato cycles) of each sample was analyzed for vibrato rate, vibrato extent, jitter (ddp), shimmer (dda), and fundamental frequency for each recording condition (wax cylinder phonograph or microphone). Steady-state and frequency-modulating sinewave test signals were also recorded under the multiple recording conditions. Results indicated no significant effect of recording condition on vibrato rate (mean [standard deviation], cylinder: 5.3 Hz [0.5], microphone: 5.3 Hz [0.5]) and no significant difference was found for mean fundamental frequency (cylinder: 389 Hz [137], microphone: 390 Hz [137]). A significant main effect of recording condition was found for vibrato extent (cylinder: ±103 cents [30], microphone: ±100 cents [31]). Additionally, mean jitter (ddp) (cylinder: 1.22% [1.09], microphone: 0.24% [0.12]) and mean shimmer (dda) (cylinder: 9.40% [4.90], microphone: 1.92% [0.94]) were significantly higher for the cylinder recording condition, indicating more cycle-to-cycle variability in the wax cylinder recorded signal. Analysis of test signals revealed similar patterns based on recording condition. This study validates past scholarly inquiry about vibrato measurements as extracted from digitized wax cylinder phonograph recordings by demonstrating that measured vibrato rate remains constant during both recording conditions. In other words, vibrato rate as measured from historical recordings can be viewed as an accurate representation of the historical singer being studied. Furthermore, it suggests that the value of prior vibrato extent measurements from these acoustic recordings may be slightly overestimated from the original voice output signals produced by singers near the beginning of the 20th century (i.e., a narrow vibrato extent might have been numerically smaller on average). Increased jitter and shimmer in the wax cylinder recording conditions may be indicative of nonlinearities in the phonograph recording or playback systems.

Discrete Fourier transform-based method for analysis of a vibrato tone

Vibrato is one of the most common musical techniques used for the enrichment of vocal and musical instrument sounds. We propose a method that can analyse the intonation, vibrato rate, and vibrato extent of a vibrato tone as a function of time, which is based on the discrete Fourier transform of its fundamental frequency trajectory. According to experimental results, the proposed method is robust to the irregularities in the fundamental frequency trajectory. In addition, the proposed method provides different results for intonation and vibrato extent from those of Prame’s method when the fundamental frequency trajectory is not perfectly sinusoidal.

A Longitudinal Ageing Analysis of Vocal Parameters of Singing Voice of Female Playback Singer

Age-related changes to the vocal structure affect the singing ability of the singer. We present a longitudinal study of vocal ageing of a female professional playback singer having more than six decades of singing span (covering singer age from 19 to 80 years). The ageing analysis is performed on six vocal parameters like – fundamental frequency (F0), vibrato, formants and spectral features like spectral roll-off and centroid. Statistical variations in these vocal parameters over the entire singing span of the singer are discussed in the paper. Significant effects noted with the ageing voice were - decrease in F0, decreased vocal range, reduction in vibrato rate, increase in vibrato extent, decrease in F2 & F4 formants and rapid change in the spectral features. This investigation also studied the effect of ageing on singing voice quality through the measurement of singing power ratio (SPR). Increase in SPR measures was observed with ageing voice. The study of impact of vocal ageing with longitudinal data on singer identification (SID) is scare. The SID experimentation performed with 350 cappella songs covering entire singing span of the singer, showed a clear impact that change in acoustical parameters with ageing affected the performance of singer identification systems.

Listener Ratings of Male Singer Technical Ability

Perceptual judgments of singer technical ability have not been widely researched. A few studies have examined perceptions of singers versus nonsingers (Usha 2017) and evaluations of vocal beauty in the male voice (Robison 1992). The investigators used recordings of male voices singing [i] in an online survey instrument using a Likert-type scale. Listeners were divided into four groups (nonmusicians, music ensemble participants, music students, and music professionals). Listeners rated the technical ability of each singer (27 recordings) on a 6-point scale from beginning to advanced. Survey responses of the four listener groups were compared with vibrato rate, extent, and jitter of the recorded samples. We hypothesized that musical training would affect how listeners rate male singers overall, with the expectation that the most musically experienced and trained listeners' ratings would be the most severe.

Comparing Contemporary Commercial and Classical Styles: Emotion Expression in Singing

This study examines the acoustic correlates of the vocal expression of emotions in contemporary commercial music (CCM) and classical styles of singing. This information may be useful in improving the training of interpretation in singing. This is an experimental comparative study. Eleven female singers with a minimum of 3 years of professional-level singing training in CCM, classical, or both styles participated. They sang the vowel [ɑ:] at three pitches (A3 220Hz, E4 330Hz, and A4 440Hz) expressing anger, sadness, joy, tenderness, and a neutral voice. Vowel samples were analyzed for fundamental frequency (fo) formant frequencies (F1-F5), sound pressure level (SPL), spectral structure (alpha ratio = SPL 1500-5000 Hz-SPL 50-1500 Hz), harmonics-to-noise ratio (HNR), perturbation (jitter, shimmer), onset and offset duration, sustain time, rate and extent of fo variation in vibrato, and rate and extent of amplitude vibrato. The parameters that were statistically significantly (RM-ANOVA, P ≤ 0.05) related to emotion expression in both genres were SPL, alpha ratio, F1, and HNR. Additionally, for CCM, significance was found in sustain time, jitter, shimmer, F2, and F4. When fo and SPL were set as covariates in the variance analysis, jitter, HNR, and F4 did not show pure dependence on expression. The alpha ratio, F1, F2, shimmer apq5, amplitude vibrato rate, and sustain time of vocalizations had emotion-related variation also independent of fo and SPL in the CCM style, while these parameters were related to fo and SPL in the classical style. The results differed somewhat for the CCM and classical styles. The alpha ratio showed less variation in the classical style, most likely reflecting the demand for a more stable voice source quality. The alpha ratio, F1, F2, shimmer, amplitude vibrato rate, and the sustain time of the vocalizations were related to fo and SPL control in the classical style. The only common independent sound parameter indicating emotional expression for both styles was SPL. The CCM style offers more freedom for expression-related changes in voice quality.

Expressing emotion through vocal performance: Acoustic cues and the effects of a mindfulness induction

Previous research suggests that musicians modulate a predictable set of acoustic cues to convey distinct emotions. The current study focuses on singers, testing the validity of cues previously reported for a wide range of instruments. The study also asks: What effect might a musician’s mindfulness have on their expressive performance? Two groups of highly skilled vocalists recorded performances of a novel melody with four distinct emotions. Prior to the performance task, an experimental group took part in a guided mindfulness induction, while a control group engaged in a self-selected relaxation activity; state mindfulness was assessed immediately after. Recordings were analyzed for tempo, temporal variation, intensity, mean centroid, vibrato rate, vibrato extent, and attack slope; individual notes with particular scale-degree functions were also compared. Results show that the two groups of participants had similar cue usage, although those in the experimental condition had higher mindfulness scores and attributed improvements in focus and awareness to the induction task. Participants as a whole used cues in the predicted directions, and significant differences were found on all acoustical measures, except vibrato rate, as a function of expressed emotion. Results also indicate that participants modified intonation to distinguish between positive and negative emotions.

Pregled istraživanja o vibratu u violinskoj interpretaciji

The subject and the goal of this paper is the research of the origin of vibrato and explanation of the experiment carried out at the Faculty of Arts in Niš. The hystorical review of the origin of vibrato and its using in various musical epochs till the present times, primarily as an ornament and then as a continuous vibrato, is given in the first part of this paper. The phenomenon of the continuous vibrato appeared gradually in the period from the end of the 19th century till the beginning of the 20th century. Various definitions of vibrato and its parameters that are characteristic for it are also given, for instance, intonation, vibrato rate and vibrato extend. The second part of this paper presents an experiment carried out at the Faculty of Arts in Nis in which students and professors participated. The aim was testing of vibrato by the objective and subjective methods. A comparative analysis of the results was also carried out. The detailed analysis has shown that these estimations were well coordinated. Thus the possibility has been opened up for using an objective estimation in education and testing the instrumentalists.

Time-scaling vibrato tones while preserving vibrato rate

Elongation of vibrato tones while preserving vibrato rate is a non-trivial problem in audio processing. It is well known that linear time-scaling in the time domain simply translates duration in lockstep with pitch. In the time/frequency domain, frequencies are preserved under linear time-scaling, but vibrato rates are not. Looping can preserve rate, but there is a problem synchronizing loops with vibrato cycles. Our current method is to parameterize harmonic frequency- and amplitude-vs-time variations so that vibrato rate is one of the parameters, along with vibrato depth and frequency drift. A heterodyne/filter method, where the heterodyne frequency is estimated from an FFT of the full-duration frequency deviation waveform, is used for vibrato analysis. Harmonic amplitude vibrato parameters can be estimated either by using the heterodyne/filter method directly or by using amplitude-vs-frequency relationships. Once the model is completed, the harmonic parameters can be time-scaled while keeping the vibrato rate intact. An exception to this treatment is to keep the attack and decay epochs intact. Once recomputed, the new time-varying harmonic spectrum representation is converted to a time-domain signal via sinusoidal additive synthesis.