Whistling in the clavichord.

Sympathetic string vibration plays an essential role in the clavichord's sound quality and tonal identity. Sympathetic vibration comes from the undamped string segments between the bridge and tuning pins. Under some conditions, a specific note, a whistling tone, stands out of the reverberation halo due to sympathetic vibration. It is hypothesized that this whistling tone comes from resonance between played and sympathetic segments of strings that are coupled through the bridge. Vibratory measurements for three pairs of excited and sympathetic strings are conducted on a copy of a historical instrument built by Hubert in 1784. The influences of bridge mobility and tuning on sympathetic string frequency and damping are studied. The results show a significant increase in vibratory amplitude, frequency veering, and damping increase in the string segments when tuning approaches frequency coincidence. Numerical simulations of a reduced clavichord model corresponding to the experiments are conducted using the modal Udwadia-Kalaba formulation. Simulation gives a more accurate picture of the veering phenomenon. Simulation and experimental results are in good agreement, showing that whistling in the clavichord comes from string resonance. It is favored by frequency coincidence between excited and sympathetic string segments and by higher bridge mobility.

Toward a physical model of the clavichord.

String excitation by the tangent in the clavichord is a unique mechanism. The tangent, keeping in contact with the string after the initial strike, continuously controls the string tension. Four main flexible subsystems are considered in the clavichord: the tangent/key subsystem, the string subsystem, the bridge-soundboard subsystem, and the string damper subsystem. A modal description of the dynamics of these subsystems is proposed. Parameters of the subsystems are estimated on a copy of a historical instrument by Hubert (1784). The different subsystems and their couplings are modeled using a modal Udwadia-Kalaba formulation. The string-tangent interaction is modeled via the intermittent contact dynamics, using the Kirchoff-Carrier string model. Realistic string, soundboard, and tangent motions are obtained using a time-domain synthesis scheme that computes the dynamics of the uncoupled subsystems and the constraints resulting from coupling between them. Simulated motions of the model in response to a driving force on the key are analyzed. The results are consistent with experimental measurements and published data on the dynamics of the clavichord. The model is able to reproduce the main acoustic features of the instrument: force on the key for intonation control, key velocity for dynamic nuances control, and constant spectral slope for varying dynamic nuances.

Perceptual equivalence of the Liljencrants-Fant and linear-filter glottal flow models.

Speech glottal flow has been predominantly described in the time-domain in past decades, the Liljencrants-Fant (LF) model being the most widely used in speech analysis and synthesis, despite its computational complexity. The causal/anti-causal linear model (LFCALM) was later introduced as a digital filter implementation of LF, a mixed-phase spectral model including both anti-causal and causal filters to model the vocal-fold open and closed phases, respectively. To further simplify computation, a causal linear model (LFLM) describes the glottal flow with a fully causal set of filters. After expressing these three models under a single analytic formulation, we assessed here their perceptual consistency, when driven by a single parameter Rd related to voice quality. All possible paired combinations of signals generated using six Rd levels for each model were presented to subjects who were asked whether the two signals in each pair differed. Model pairs LFLM-LFCALM were judged similar when sharing the same Rd value, and LF was considered the same as LFLM and LFCALM given a consistent shift in Rd. Overall, the similarity between these models encourages the use of the simpler and more computationally efficient models LFCALM and LFLM in speech synthesis applications.

Paradigmatic variation of vowels in expressive speech: Acoustic description and dimensional analysis.

Acoustic variation in expressive speech at the syllable level is studied. As emotions or attitudes can be conveyed by short spoken words, analysis of paradigmatic variations in vowels is an important issue to characterize the expressive content of such speech segments. The corpus contains 160 sentences produced under seven expressive conditions (Neutral, Anger, Fear, Surprise, Sensuality, Joy, Sadness) acted by a French female speaker (a total of 1120 sentences, 13 140 vowels). Eleven base acoustic parameters are selected for voice source and vocal tract related feature analysis. An acoustic description of the expressions is drawn, using the dimensions of melodic range, intensity, noise, spectral tilt, vocalic space, and dynamic features. The first three functions of a discriminant analysis explain 95% of the variance in the data. These statistical dimensions are consistently associated with acoustic dimensions. Covariation of intensity and F0 explains over 80% of the variance, followed by noise features (8%), covariation of spectral tilt, and F0 (7%). On the basis of isolated vowels alone, expressions are classified with a mean accuracy of 78%.

Drawing melodies: evaluation of chironomic singing synthesis.

Cantor Digitalis, a real-time formant synthesizer controlled by a graphic tablet and a stylus, is used for assessment of melodic precision and accuracy in singing synthesis. Melodic accuracy and precision are measured in three experiments for groups of 20 and 28 subjects. The task of the subjects is to sing musical intervals and short melodies, at various tempi, using chironomy (hand-controlled singing), mute chironomy (without audio feedback), and their own voices. The results show the high accuracy and precision obtained by all the subjects for chironomic control of singing synthesis. Some subjects performed significantly better in chironomic singing compared to natural singing, although other subjects showed comparable proficiency. For the chironomic condition, mean note accuracy is less than 12 cents and mean interval accuracy is less than 25 cents for all the subjects. Comparing chironomy and mute chironomy shows that the skills used for writing and drawing are used for chironomic singing, but that the audio feedback helps in interval accuracy. Analysis of blind chironomy (without visual reference) indicates that a visual feedback helps greatly in both note and interval accuracy and precision. This study demonstrates the capabilities of chironomy as a precise and accurate mean for controlling singing synthesis.

Chironomic stylization of intonation.

Intonation stylization is studied using "chironomy," i.e., the analogy between hand gestures and prosodic movements. An intonation mimicking paradigm is used. The task of the ten subjects is to copy the intonation pattern of sentences with the help of a stylus on a graphic tablet, using a system for real-time manual intonation modification. Gestural imitation is compared to vocal imitation of the same sentences (seven for a male speaker, seven for a female speaker). Distance measures between gestural copies, vocal imitations, and original sentences are computed for performance assessment. Perceptual testing is also used for assessing the quality of gestural copies. The perceptual difference between natural and stylized contours is measured using a mean opinion score paradigm for 15 subjects. The results indicate that intonation contours can be stylized with accuracy by chironomic imitation. The results of vocal imitation and chironomic imitation are comparable, but subjects show better imitation results in vocal imitation. The best stylized contours using chironomy seems perceptually indistinguishable or almost indistinguishable from natural contours, particularly for female speech. This indicates that chironomic stylization is effective, and that hand movements can be analogous to intonation movements.

On the dynamics of the clavichord: from tangent motion to sound.

An experimental study of variations in the sound of clavichord notes at different dynamic levels is described. Radiated acoustic signal, tangent velocity and two tangent-string contact signals are synchronously measured for all 51 notes of an unfretted instrument. More than ten repeated measures are recorded in order to obtain as much variation in dynamic level as possible. The tangent motion, expressed in terms of velocity, is studied in the time and frequency domains. A model of the tangent-string contact point velocity is proposed. Then, three aspects of the sounded tones are analyzed: SPL and its relationship to tangent velocity, spectral slope, and pitch variations. These results indicate a linear relationship between sound pressure level and tangent peak log velocity. Spectral slope seems almost constant independent of tangent velocity and dynamic level. Both tangent velocity and finger pressure are shown to influence the fundamental frequency. In conclusion, controlling both finger velocity and finger pressure may prove challenging for the player, and this may explain why the sound quality of the clavichord depends so much on the players ability.

Glottal open quotient in singing: measurements and correlation with laryngeal mechanisms, vocal intensity, and fundamental frequency.

This article presents the results of glottal open-quotient measurements in the case of singing voice production. It explores the relationship between open quotient and laryngeal mechanisms, vocal intensity, and fundamental frequency. The audio and electroglottographic signals of 18 classically trained male and female singers were recorded and analyzed with regard to vocal intensity, fundamental frequency, and open quotient. Fundamental frequency and open quotient are derived from the differentiated electroglottographic signal, using the DECOM (DEgg Correlation-based Open quotient Measurement) method. As male and female phonation may differ in respect to vocal-fold vibratory properties, a distinction is made between two different glottal configurations, which are called laryngeal mechanisms: mechanism 1 (related to chest, modal, and male head register) and mechanism 2 (related to falsetto for male and head register for female). The results show that open quotient depends on the laryngeal mechanisms. It ranges from 0.3 to 0.8 in mechanism 1 and from 0.5 to 0.95 in mechanism 2. The open quotient is strongly related to vocal intensity in mechanism 1 and to fundamental frequency in mechanism 2.

On the use of the derivative of electroglottographic signals for characterization of nonpathological phonation.

Electroglottography is a common method for providing noninvasive measurements of glottal activity. The derivative of the electroglottographic signal, however, has not attracted much attention, although it yields reliable indicators of glottal closing instants. The purpose of this paper is to provide a guide to the usefulness of this signal. The main features that are to be found in this signal are presented on the basis of an extensive analysis of a database of items sung by 18 trained singers. Glottal opening and closing instants are related to peaks in the signal; the latter can be used to measure glottal parameters such as fundamental frequency and open quotient. In some cases, peaks are doubled or imprecise, which points to special (but by no means uncommon) glottal configurations. A correlation-based algorithm for the automatic measurement of fundamental frequency and open quotient using the derivative of electroglottographic signals is proposed. It is compared to three other electroglottographic-based methods with regard to the measurement of open quotient in inverse-filtered derived glottal flow. It is shown that agreement with the glottal-flow measurements is much better than most threshold-based measurements in the case of sustained sounds.

Just noticeable differences of open quotient and asymmetry coefficient in singing voice.

This study aims to explore the perceptual relevance of the variations of glottal flow parameters and to what extent a small variation can be detected. Just Noticeable Differences (JNDs) have been measured for three values of open quotient (0.4, 0.6, and 0.8) and two values of asymmetry coefficient (2/3 and 0.8), and the effect of changes of vowel, pitch, vibrato, and amplitude parameters has been tested. Two main groups of subjects have been analyzed: a group of 20 untrained subjects and a group of 10 trained subjects. The results show that the JND for open quotient is highly dependent on the target value: an increase of the JND is noticed when the open quotient target value is increased. The relative JND is constant: deltaOq/Oq = 14% for the untrained and 10% for the trained. In the same way, the JND for asymmetry coefficient is also slightly dependent on the target value--an increase of the asymmetry coefficient value leads to a decrease of the JND. The results show that there is no effect from the selected vowel or frequency (two values have been tested), but that the addition of a vibrato has a small effect on the JND of open quotient. The choice of an amplitude parameter also has a great effect on the JND of open quotient.