Harmonic Mistuning Research Articles

Differences in Auditory Perception Between Young and Older Adults When Controlling for Differences in Hearing Loss and Cognition.

This study was designed to examine age effects on various auditory perceptual skills using a large group of listeners (155 adults, 121 aged 60–88 years and 34 aged 18–30 years), while controlling for the factors of hearing loss and working memory (WM). All subjects completed 3 measures of WM, 7 psychoacoustic tasks (24 conditions) and a hearing assessment. Psychophysical measures were selected to tap phenomena thought to be mediated by higher-level auditory function and included modulation detection, modulation detection interference, informational masking (IM), masking level difference (MLD), anisochrony detection, harmonic mistuning, and stream segregation. Principal-components analysis (PCA) was applied to each psychoacoustic test. For 6 of the 7 tasks, a single component represented performance across the multiple stimulus conditions well, whereas the modulation-detection interference (MDI) task required two components to do so. The effect of age was analyzed using a general linear model applied to each psychoacoustic component. Once hearing loss and WM were accounted for as covariates in the analyses, estimated marginal mean thresholds were lower for older adults on tasks based on temporal processing. When evaluated separately, hearing loss led to poorer performance on roughly 1/2 the tasks and declines in WM accounted for poorer performance on 6 of the 8 psychoacoustic components. These results make clear the need to interpret age-group differences in performance on psychoacoustic tasks in light of cognitive declines commonly associated with aging, and point to hearing loss and cognitive declines as negatively influencing auditory perceptual skills.

Intentional Response Reduction by Harmonic Mistuning of Bladed Disks With Aerodynamic Damping

A harmonic mistuning concept for bladed disks is analyzed in order to intentionally reduce the forced response of specific modes below their tuned amplitude level. By splitting a mode pair associated with a specific nodal diameter pattern, the lightly damped traveling wave mode of the nominally tuned blisk is superposed with its counter-rotating complement. Consequently, a standing wave is formed in which the former wave train benefits from an increase in aerodynamic damping. Unlike previous analyses of randomly perturbed configurations, the mode-specific stabilization is intentionally promoted through adjusting the harmonic content of the mistuning pattern (MT). Through a reorientation of the localized mode shapes in relation to the discrete blades, the response is additionally attenuated by an amount of up to 7.6%. The achievable level of amplitude reduction is analytically predicted based on the properties of the tuned system. Furthermore, the required degree of mistuning for a sufficient separation of a mode pair is derived.

Mistuning detection performance of ferrets in a go/no-go task.

The harmonic structure of sounds is an important grouping cue in auditory scene analysis. The ability of ferrets to detect mistuned harmonics was measured using a go/no-go task paradigm. Psychometric functions plotting sensitivity as a function of degree of mistuning were used to evaluate behavioral performance using signal detection theory. The mean (± standard error of the mean) threshold for mistuning detection was 0.8 ± 0.1 Hz, with sensitivity indices and reaction times depending on the degree of mistuning. These data provide a basis for investigation of the neural basis for the perception of complex sounds in ferrets, an increasingly used animal model in auditory research.

A Method to Reduce the Energy Localization in Mistuned Bladed Disks by Application-Specific Blade Pattern Arrangement

The focus of the paper is the analysis of mistuning, which are small deviations of the blade properties, e.g., due to manufacturing tolerances. The resonant amplitudes of turbine blades are very sensitive to these deviations which can lead to significantly increased vibratory response of some blades with the increased risk of high cycle fatigue. The main part of the paper discusses about the methods that can be used to find blade patterns which are insensitive to energy localization. The sensitivity of the forced response against harmonic mistuning, which is a harmonic alignment of the blades respective to the mistuning factors of the single blades, is examined. A previously developed reduced order model (ROM) is used to efficiently conduct Monte Carlo simulations (MCSs). Especially the influence of the variance of the harmonically mistuned blade patterns is discussed. On the basis of this analysis, rules are developed to suppress the energy localization. The rules are mainly focused on the alignment of the blades around the bladed disk. The approach also takes advantage of the special properties of harmonic mistuning patterns. An assignment of the blades to insensitive harmonic mistuning patterns with a specific variance and number of periods is used to reduce the maximum of the amplification factor of the forced response. A similar approach uses intentional mistuning patterns with different blade types which are aligned harmonically and are insensitive to an additional stochastic mistuning. In case of specific combinations of the dependent parameters, especially the variance of the mistuning factors and the number of periods, the energy localization can be reduced considerably.

Harmonic Mistuning of Blisks

AbstractThe paper describes a new method to calculate the maximum amplificationof blade vibrations of a bladed disk or blisk subject to manufacturing tolerances. Two effects of mistuned blisks are analyzed in this paper. The separation of two orthogonal nodal diameters are shown and described in detail. Furthermore, the excitation of more than one nodal diameter by only one engine order is discussed. If the eigenfrequencies of these nodal diameters are close together, the vibration amplitude of some blades increases. Based on a lumped‐mass model, it is shown which maximum amplitude can occur. The idea is to use a harmonic mistuning pattern to get the highest influence at small tolerances for one single nodal diameter. This influence is not exceeded by a randomly mistuned system and limits the maximum amplitude. The given analysis is validated by a common Monte‐Carlo simulation. On the other hand, a description of the excitation of other nodal diameters is given. Using these two effects, an absolute vibration maximum for a given mistuning limit can be calculated. (© 2015 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Cortical representations sensitive to the number of perceived auditory objects emerge between 2 and 4 months of age: electrophysiological evidence.

Sound waves emitted by two or more simultaneous sources reach the ear as one complex waveform. Auditory scene analysis involves parsing a complex waveform into separate perceptual representations of the sound sources [Bregman, A. S. Auditory scene analysis: The perceptual organization of sounds. London: MIT Press, 1990]. Harmonicity provides an important cue for auditory scene analysis. Normally, harmonics at integer multiples of a fundamental frequency are perceived as one sound with a pitch corresponding to the fundamental frequency. However, when one harmonic in such a complex, pitch-evoking sound is sufficiently mistuned, that harmonic emerges from the complex tone and is perceived as a separate auditory object. Previous work has shown that the percept of two objects is indexed in both children and adults by the object-related negativity component of the ERP derived from EEG recordings [Alain, C., Arnott, S. T., & Picton, T. W. Bottom-up and top-down influences on auditory scene analysis: Evidence from event-related brain potentials. Journal of Experimental Psychology: Human Perception and Performance, 27, 1072-1089, 2001]. Here we examine the emergence of object-related responses to an 8% harmonic mistuning in infants between 2 and 12 months of age. Two-month-old infants showed no significant object-related response. However, in 4- to 12-month-old infants, a significant frontally positive component was present, and by 8-12 months, a significant frontocentral object-related negativity was present, similar to that seen in older children and adults. This is in accordance with previous research demonstrating that infants younger than 4 months of age do not integrate harmonic information to perceive pitch when the fundamental is missing [He, C., Hotson, L., & Trainor, L. J. Maturation of cortical mismatch mismatch responses to occasional pitch change in early infancy: Effects of presentation rate and magnitude of change. Neuropsychologia, 47, 218-229, 2009]. The results indicate that the ability to use harmonic information to segregate simultaneous sounds emerges at the cortical level between 2 and 4 months of age.

Neural Correlates of Auditory Scene Analysis Based on Inharmonicity in Monkey Primary Auditory Cortex

Segregation of concurrent sounds in complex acoustic environments is a fundamental feature of auditory scene analysis. A powerful cue used by the auditory system to segregate concurrent sounds, such as speakers' voices at a cocktail party, is inharmonicity. This can be demonstrated when a component of a harmonic complex tone is perceived as a separate tone "popping out" from the complex as a whole when it is sufficiently mistuned from its harmonic value. The neural bases of perceptual "pop out" of mistuned harmonics are unclear. We recorded multiunit activity from primary auditory cortex (A1) of behaving monkeys elicited by harmonic complex tones that were either "in tune" or that contained a mistuned third harmonic set at the best frequency of the neural populations. Responses to mistuned sounds were enhanced relative to responses to "in-tune" sounds, thus correlating with the enhanced perceptual salience of the mistuned component. Consistent with human psychophysics of "pop out," response enhancements increased with the degree of mistuning, were maximal for neural populations tuned to the frequency of the mistuned component, and were not observed under comparable stimulus conditions that do not elicit perceptual "pop out." Mistuning was also associated with changes in neuronal temporal response patterns phase locked to "beats" in the stimuli. Intracortical auditory evoked potentials paralleled noninvasive neurophysiological correlates of perceptual "pop out" in humans, further augmenting the translational relevance of the results. Findings suggest two complementary neural mechanisms for "pop out," based on the detection of local differences in activation level or coherence of temporal response patterns across A1.

Mistuning in two-part singing

This research describes the strategy of singers in reacting to the pitch deviation from equally tempered (ET) value in their ensemble partner's part in singing two-part a cappella music, and the ability of professional musicians to identify such deviations. Professional singers preferred to maintain the purity of melodic intervals in their own part and to ignore the occurring harmonic mistuning with their deviating ensemble partner. In multi-part singing, the musical interval perception ability of the singers is more finely honed for production than it is for perception, which can be explained by the enhancing effect of the memory of how to vocally produce the intervals, available only in the process of singing.

Graded cue information in dichotic pitch: effects on event-related potentials

To determine whether electroencephalogram components elicited by dichotic pitch stimuli are all-or-none threshold-like responses or graded responses that depend on the saliency of the stimuli, we recorded electroencephalograms while participants listened to dichotic pitch stimuli constructed with different signal-to-background ratios. The object-related negativity and P400 components were largest when the dichotic pitch was most salient (high signal-to-background ratio), and decreased in amplitude with decreasing signal-to-background ratio. These results are similar to those reported for mistuned harmonics, thereby providing additional evidence that the object-related negativity and P400 components observed for these disparate stimulus types reflect similar processing. They also support the notion that the object-related negativity and P400 amplitudes are dependent on the level of relevant cue-based stimulus information.

Forced Response of Turbine Engine Bladed Disks and Sensitivity to Harmonic Mistuning

The mistuned forced response of turbine engine bladed disks is treated using harmonic perturbations in the properties of a continuous ring. A continuous shear spring is attached to the ring in which the stiffness is allowed to vary along the ring annulus. The modes of such a structure with a single harmonic mistuning pattern are shown to obey the Mathieu equation, which is solved to obtain the natural frequencies and modes of the mistuned system. The forced response of the system is then examined to determine the sensitivity of the system to small mistuning. The model is extended to include multiple harmonics, allowing for the possibility of general mistuning. An expression for the maximum amplitude magnification due to small mistuning is developed by showing that high response is caused by distortion of the structural modes. A method to intentionally mistune systems for maximum forced response is demonstrated, and numerical results demonstrate the accuracy of the analytical prediction. The intentionally mistuned system response is shown to be robust with respect to small random mistuning. Such a result might be useful for designing a test rotor for screening new bladed disk designs or for establishing the root cause of fatigue problems.

Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana).

The ability of 73 male bullfrogs (Rana catesbeiana) to detect single mistuned harmonics in an otherwise periodic signal was studied. Bullfrogs in their natural environment were presented with playbacks of synthetic signals, resembling their species advertisement calls, that differed in the frequency of 1 harmonic component (out of 22). There were significant differences in the number and latency of the males' evoked vocal responses to these stimuli, suggesting that males were sensitive to the differences between the sounds. Differences in envelope shape (rate and depth of amplitude modulation) produced by the harmonic mistunings may underlie the differences in response. Frogs, like birds and humans, can discriminate sounds on the basis of harmonic structure, indicating that this is a general perceptual trait shared among vertebrates.

Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana).

Perception of mistuned harmonics in complex sounds by the bullfrog (Rana catesbeiana).

On the Forced Response of Harmonically and PartiallyMistuned Bladed Disks. Part I: Harmonic Mistuning

This series of two papers focuses on the determination and clarification of the characteristics of the forced response of bladed disks that exhibit a mistuning pattern that is either harmonic or partial. Harmonic mistuning refers to single wavelength variations in structural properties along the disk while partial mistuning is associated with blade characteristics that are random in a specific sector and tuned elsewhere. The results of this analysis demonstrate that many features of the response of these simple systems match not only qualitatively but also quantitatively their counterparts on randomly mistuned bladed disks. Relying on these similarities, simple and reliable approximations of the localization factor and of the mean response are easily derived that exemplify the usefulness of harmonic and partial mistuning patterns. Finally, it is demonstrated both theoretically and by comparison with simulation results that the maximum amplitude of response of a disk closely follows a Weibull‐type distribution in all coupling situations, from very weak to very strong.

On the Forced Response of Harmonically and Partially MistunedBladed Disks. Part II: Partial Mistuning and Applications

This series of two papers focuses on the determination and clarification of the characteristics of the forced response of bladed disks that exhibit a mistuning pattern that is either harmonic or partial. Harmonic mistuning refers to single wavelength variations in structural properties along the disk while partial mistuning is associated with blade characteristics that are random in a specific sector and tuned elsewhere. The results of this analysis demonstrate that many features of the response of these simple systems match not only qualitatively but also quantitatively their counterparts on randomly mistuned bladed disks. Relying on these similarities, simple and reliable approximations of the localization factor and of the mean response are easily derived that exemplify the usefulness of harmonic and partial mistuning patterns. Finally, it is demonstrated both theoretically and by comparison with simulation results that the maximum amplitude of response of a disk closely follows a Weibull‐type distribution in all coupling situations, from very weak to very strong.

The pitch of a mistuned harmonic: evidence for a template model.

A harmonic of a periodic complex tone can be heard out as a separate entity if the harmonic is slightly mistuned from its correct frequency. Pitch matching experiments show that the pitch of such a mistuned harmonic differs systematically from its frequency. The shift in pitch is found to be an exaggeration of the frequency mistuning. This article considers two classes of model for the pitch shift. In the first class are tonotopically local interaction models which attribute the pitch shift to interactions between the mistuned harmonic and neighboring harmonics, where the neighborhood is established by peripheral filtering. The second class of model attributes the pitch shift to a contrast between the mistuned harmonic and a broadband harmonic template. This article describes six pitch matching experiments using complex tones having spectral gaps, strategically chosen to compare local interaction and template models. The results show that when a competition is set up between local interactions and a template, the template proves to be dominant. A parallel between the pitch shifts of mistuned harmonics and periodicity pitch, also attributed to a harmonic template, is seen as the frequency range of the mistuned harmonic is changed. Tonotopically local influences are evident in several experiments, but they are of secondary importance.

The pitches of mistuned harmonics

If a single harmonic of a complex tone is mistuned it can be heard as a separate entity. Pitch matching experiments show that the pitch of a mistuned harmonic does not agree with its frequency. The shift in pitch, caused by the complex context, is an exaggeration of the frequency mistuning. The differential pitch shift, for positive versus negative mistuning, is called the ‘‘split.’’ Splits for complex tones with simple spectra were measured by Hartmann and Smith [J. Acoust. Soc. Am. Suppl. 1 85, S109 (1989)]. Experiments reported here, measure splits for complex tones having spectral gaps and other anomalies. Experiments show that splits depend upon partial masking: Components below the mistuned harmonic create large splits; splits increase with increasing stimulus level. Experiments show that splits also depend upon the overall periodicity of the complex: Splits are larger for mistuned harmonics than for nonharmonic interstitials, given identical local spectral environments. Splits are larger for mistuned harmonics with low harmonic number or low fundamental frequency. These observations require revision of the neural timing model for the pitches of mistuned harmonics. [Work supported by the NIDCD, DC00181.]

Anomalies in the neural tonotopic-synchrony pattern as the basis for the segregation of tones

It is possible to envision a comprehensive model for the segregation and integration of tones based upon synchrony and asynchrony of neural excitation patterns. Evidence for this model comes from experiments on mistuned harmonic matching, simultaneous and sequential octave tuning, and FM incoherence detection with harmonic and inharmonic tones. Such a model has the conceptual advantage of unifying temporal effects and mistuning effects upon segregation. A central remaining question in the formulation of this model is the role of tonotopic analysis. There is, in fact, tonal segregation attributable entirely to tonotopic oddity. More than that, there are tonotopic effects on the processing of synchrony anomalies. These can be seen in mistuned harmonic detection experiments with neighboring harmonics removed, or with added constant remote inharmonic confuser, or with several mistuned harmonics that are themselves either mutually synchronous or asynchronous. Such experiments have suggested a tuned-autocorrelator model with a bandwidth of about two critical bands. Tonotopically based synchrony models are, in turn, challenged by experiments on cross-channel interaction where excitation at intervening tonotopic sites has been deliberately squelched. [Work supported by the NIDCD, DC 00181.]

Hearing a mistuned harmonic in an otherwise periodic complex tone

The ability of a listener to detect a mistuned harmonic in an otherwise periodic tone is representative of the capacity to segregate auditory entities on the basis of steady-state signal cues. By use of a task in which listeners matched the pitch of a mistuned harmonic, this ability has been studied, in order to find dependences on mistuned harmonic number, fundamental frequency, signal level, and signal duration. The results considerably augment the data previously obtained from discrimination experiments and from experiments in which listeners counted apparent sources. Although previous work has emphasized the role of spectral resolution in the segregation process, the present work suggests that neural synchrony is an important consideration; our data show that listeners lose the ability to segregate mistuned harmonics at high frequencies where synchronous neural firing vanishes. The functional form of this loss is insensitive to the spacing of the harmonics. The matching experiment also permits the measurement of the pitches of mistuned harmonics. The data exhibit shifts of a form that argues against models of pitch shifts that are based entirely upon partial masking.

On the pitch of mistuned harmonics in a complex tone

Four listeners matched the pitch of a single mistuned harmonic in an otherwise periodic complex tone, whose fundamental frequency was near 200 Hz. In individual experiments, harmonics numbers 1, 2, 3, 4, 5, 7, 9, and 11 were individually mistuned, by 11 different amounts ranging from − 8% to + 8%. The experiment thus measured the shift in the pitch of a sine component caused by other components of the complex tone. The experiments showed that for mistuned low-order harmonics a positive mistuning produces a positive pitch shift while a negative mistuning produces a negative pitch shift. For mistuned high-order harmonics the pattern is similar except that the pitch shifts caused by positive mistunings become large. These data were compared with a place theory in which the peak in the excitation pattern for an individual harmonic is partially masked by peaks due to neighboring harmonics. Although the model correctly predicts the results for positive mistunings, it fails dramatically for negative mistunings. The data are also compared with a theory whereby pitch is determined by peaks in an interspike-interval histogram per the MIT model. This theory can account for all the data, except for the mistuned fundamental, though filter bandwidths must be considerably enlarged compared to the MIT model to obtain agreement. [Work supported by the National Institutes of Health.]

Matching the pitch of a mistuned harmonic in an otherwise periodic complex tone

Listeners adjusted the frequency of a sine tone to match the pitch of a single mistuned harmonic in a complex tone consisting of 16 harmonics. Fundamental frequencies were 200, 400, or 800 Hz, and mistunings ranged from 0.5% to 8.0%. The successful matches, those close to the actual mistuned harmonic, show highly consistent and unexpected pitch shift effects; the pitch shifts can be twice as large as the frequency shifts, for both positive and negative frequency shifts. The percentage of matches which are successful provides an estimate of a listener's ability to segregate the mistuned component from the complex tone. Best performance occurs for mistuned harmonics in the region of spectral dominance. The highest frequency which can be segregated is a decreasing function of the fundamental frequency. The latter result suggests that the segregation operation depends upon both place and time coding in the auditory system. [Work supported by the NIH, the NSF, and the CHRS—France.]