Harmonic Tones Research Articles

Time-Resolved Flowfield and Acoustic Measurements of a Ducted and Unducted Rotor

The impact of adding a duct to an 18.5″ diameter, triple-bladed, electrically driven rotor operating up to Mtip=0.5 at static conditions is investigated experimentally to identify the source mechanisms governing the measured acoustic differences. An unducted rotor is characterized by strong, coherent tip vorticity that interacts with each blade passing, generating high-amplitude harmonic tones. The addition of the duct results in tonal broadening and an increase of the primary and harmonic tone amplitudes. Up to a 15 dB increase in broadband noise across the entire frequency range is measured. High-speed particle imaging velocimetry up to 6.4 kHz is employed to acquire phase-locked and ensemble-averaged measurements of the velocity, vorticity, and turbulence fields. While it is often theorized that a duct can shield lateral acoustic radiation, this study finds that the ducted rotor is louder across all operating regimes, and the noise increases with tip Mach number. The ducted rotor dissipates the coherent tip vorticity into incoherent turbulence intensity due to the interaction of the vortices with the duct internal walls, contributing to a strong broadband noise increase and tonal broadening. The ducted rotor broadband noise increase is due to the rotor interacting with a more turbulent inflow condition and increased turbulence intensity throughout the plume shear layer.

Timbral brightness perception investigated through multimodal interference

Brightness is among the most studied aspects of timbre perception. Psychoacoustically, sounds described as “bright” versus “dark” typically exhibit a high versus low frequency emphasis in the spectrum. However, relatively little is known about the neurocognitive mechanisms that facilitate these metaphors we listen with. Do they originate in universal magnitude representations common to more than one sensory modality? Triangulating three different interaction paradigms, we investigated using speeded classification whether intramodal, crossmodal, and amodal interference occurs when timbral brightness, as modeled by the centroid of the spectral envelope, and pitch height/visual brightness/numerical value processing are semantically congruent and incongruent. In four online experiments varying in priming strategy, onset timing, and response deadline, 189 total participants were presented with a baseline stimulus (a pitch, gray square, or numeral) then asked to quickly identify a target stimulus that is higher/lower, brighter/darker, or greater/less than the baseline after being primed with a bright or dark synthetic harmonic tone. Results suggest that timbral brightness modulates the perception of pitch and possibly visual brightness, but not numerical value. Semantically incongruent pitch height-timbral brightness shifts produced significantly slower reaction time (RT) and higher error compared to congruent pairs. In the visual task, incongruent pairings of gray squares and tones elicited slower RTs than congruent pairings (in two experiments). No interference was observed in the number comparison task. These findings shed light on the embodied and multimodal nature of experiencing timbre.

The potential role of insolation in the long-term climate evolution since the early Pleistocene

The distribution of insolation over time and space is a significant driver of climate change on orbital timescales. However, the influence of insolation on long-term climate evolution remains poorly understood due to the absence of a discernible long-term trend regulated by Earth's orbit. In this study, we present a sea surface temperature anomaly (SSTA) stack spanning the past 2 Myr, compiled from 26 millennial-resolved records obtained from the global ocean. The global average sea surface temperature (SST) reveals a 405-kyr cycle, as well as a gradual decrease of 2.34 ± 1.05 °C (1σ) from 2000 ka to 940 ka, followed by a period of relative stability. We introduce an index named the integral of annual mean insolation anomaly (IAMIA), which quantifies the continuous departure of annual mean insolation (AMI) from its “normal” cycle over a specific time interval. We find that the SST leads the variations in AMI and IAMIA at the 405-kyr band, intimating that the cycle evident in global SST does not originate from the changes of eccentricity but rather stems from harmonic or combination tones. Notably, IAMIA exhibits a fundamental shift at 935 ka, coinciding with the “900-ka event” observed in the SST. Modeling results support that the “900-ka event” could be driven by the change of cumulative insolation. Additionally, IAMIA underscores the important role of insolation in Pleistocene climate change on the long-term trend through the cumulative response of ocean heat content (OHC) to successive small step-wise insolation changes. Furthermore, we hypothesize that the fundamental changes of insolation around 935 ka, transitioning from a positive state characterized by substantial amplitude to a negative state typified by diminished amplitude, facilitated the onset and progression of the mid-Pleistocene transition (MPT). This investigation provides invaluable insights into the role of insolation in long-term climate evolution.

A psychoacoustic test on the effect of masking on annoyance to urban air mobility vehicle noise

Urban Air Mobility (UAM) vehicles have a large range of designs and configurations that lead to new noise characteristics and potentially different perceptual responses when compared to traditional aircraft. In addition, UAM vehicles are expected to operate around and within densely populated regions where the presence of ambient background noise is often present. Strategically, this can be leveraged to inform vehicle design and operations to partially or completely mask UAM noise, allowing for mitigation of negative responses and an increased number of allowed operations. A psychoacoustic test was conducted to investigate how masking effects can influence the annoyance response to a low frequency harmonic tone complex (80-320 Hz). To do this, five test subjects compared their annoyance response to the low frequency tonal noise with a higher frequency broadband noise (10 dB down bandwidth between 300 and 2000 Hz), with and without a masking noise present. Detection thresholds were also measured for both sounds to help fit a model to the data. Although the effect of masking on annoyance is complex, results indicate that for some individuals, masking leads to a lower annoyance than the sound level alone would predict.

Benefits of Harmonicity for Hearing in Noise Are Limited to Detection and Pitch-Related Discrimination Tasks.

Harmonic complex tones are easier to detect in noise than inharmonic complex tones, providing a potential perceptual advantage in complex auditory environments. Here, we explored whether the harmonic advantage extends to other auditory tasks that are important for navigating a noisy auditory environment, such as amplitude- and frequency-modulation detection. Sixty young normal-hearing listeners were tested, divided into two equal groups with and without musical training. Consistent with earlier studies, harmonic tones were easier to detect in noise than inharmonic tones, with a signal-to-noise ratio (SNR) advantage of about 2.5 dB, and the pitch discrimination of the harmonic tones was more accurate than that of inharmonic tones, even after differences in audibility were accounted for. In contrast, neither amplitude- nor frequency-modulation detection was superior with harmonic tones once differences in audibility were accounted for. Musical training was associated with better performance only in pitch-discrimination and frequency-modulation-detection tasks. The results confirm a detection and pitch-perception advantage for harmonic tones but reveal that the harmonic benefits do not extend to suprathreshold tasks that do not rely on extracting the fundamental frequency. A general theory is proposed that may account for the effects of both noise and memory on pitch-discrimination differences between harmonic and inharmonic tones.

Cochlear implant pitch and lexical tone perception in quiet and noise using F0-rate coding

Fundamental frequency (F0) cues to voice/musical pitch can be coded by pulse-rate or amplitude modulation (AM) rate of electrical pulse-trains in cochlear implant (CI) systems. However, for most clinical strategies (e.g., ACE), temporal cues to F0 are often poorly coded, particularly for female and children's voices and/or in background noise. Strategies such as Optimized Pitch And Language (OPAL) and Fundamental Asynchronous Stimulus Timing (FAST) enhance temporal F0 cues. For OPAL, F0 is estimated and used to control the AM rate coded by electrical pulse-trains in channel containing harmonics of F0. Significant benefits of OPAL to pitch ranking, speech intonation, and Mandarin lexical tone recognition have been observed compared to ACE. For FAST, peak-timing information in channel envelopes is used to derive pulse-timing in each channel and therefore much lower stimulation rates are provided resulting in longer battery life. In bilateral CI systems, it provides better ITD sensitivity, lateralization, and spatial release from masking compared to ACE. Presented here are the results of two studies, the first explored pitch perception of harmonic tones presented in quiet and noise using experimental OPAL and FAST strategies, and the second examined Mandarin lexical tone perception in quiet and noise using ACE and OPAL in a clinical processor.

Vibration-reduced anxiety-like behavior relies on ameliorating abnormalities of the somatosensory cortex and medial prefrontal cortex.

Abstract JOURNAL/nrgr/04.03/01300535-202406000-00040/inline-graphic1/v/2023-10-30T152229Z/r/image-tiff Tibetan singing bowls emit low-frequency sounds and produce perceptible harmonic tones and vibrations through manual tapping. The sounds the singing bowls produce have been shown to enhance relaxation and reduce anxiety. However, the underlying mechanism remains unclear. In this study, we used chronic restraint stress or sleep deprivation to establish mouse models of anxiety that exhibit anxiety-like behaviors. We then supplied treatment with singing bowls in a bottomless cage placed on the top of a cushion. We found that unlike in humans, the combination of harmonic tones and vibrations did not improve anxiety-like behaviors in mice, while individual vibration components did. Additionally, the vibration of singing bowls increased the level of N-methyl-D-aspartate receptor 1 in the somatosensory cortex and prefrontal cortex of the mice, decreased the level of γ-aminobutyric acid A (GABA) receptor α 1 subtype, reduced the level of CaMKII in the prefrontal cortex, and increased the number of GABAergic interneurons. At the same time, electrophysiological tests showed that the vibration of singing bowls significantly reduced the abnormal low-frequency gamma oscillation peak frequency in the medial prefrontal cortex caused by stress restraint pressure and sleep deprivation. Results from this study indicate that the vibration of singing bowls can alleviate anxiety-like behaviors by reducing abnormal molecular and electrophysiological events in somatosensory and medial prefrontal cortex.

Simulation of hearing loss can induce pitch shifts for complex tones.

Most studies on pitch shift provoked by hearing loss have been conducted using pure tones. However, many sounds encountered in everyday life are harmonic complex tones. In the present study, psychoacoustic experiments using complex tones were performed on healthy participants, and the possible mechanisms that cause pitch shift due to hearing loss are discussed. Two experiments were performed in this study. In experiment 1, two tones were presented, and the participants were asked to select the tone that was higher in pitch. Partials with frequencies less than 250, 500, 750, or 1,000 Hz were eliminated from the harmonic complex tones and used as test tones to simulate low-tone hearing loss. Each tone pair was constructed such that the tone with a lower fundamental frequency (F0) was higher in terms of the frequency of the lowest partial. Furthermore, partials whose frequencies were greater than 1,300 or 1,600 Hz were also eliminated from these test tones to simulate high-tone hearing loss or modified sounds that patients may hear in everyday life. When a tone with a lower F0 was perceived as higher in pitch, it was considered a pitch shift from the expected tone. In experiment 2, tonal sequences were constructed to create a passage of the song "Lightly Row." Similar to experiment 1, partials of harmonic complex tones were eliminated from the tones. After listening to these tonal sequences, the participants were asked if the sequences sounded correct based on the melody or off-key. The results showed that pitch shifts and the melody sound off-key when lower partials are eliminated from complex tones, especially when a greater number of high-frequency components are eliminated. Considering that these experiments were performed on healthy participants, the results suggest that the pitch shifts from the expected tone when patients with hearing loss hear certain complex tones, regardless of the underlying etiology of the hearing loss.

Automated cataloging of oyster toadfish (Opsanus tau) boatwhistle calls using template matching and machine learning

Oyster toadfish (Opsanus tau) represent an ecologically significant species found throughout estuaries along the eastern coast of the United States. While these crevice-dwelling fish can be challenging to observe in their habitats, it is possible to infer their distribution and aspects of their behavior by recording the sounds they produce. The task of cataloging the distinctive advertisement boatwhistle sounds produced by male toadfish to attract females throughout the spring and summer is automated using a multi-step process. Candidate boatwhistles are first identified by template matching using a suite of synthetic spectrogram kernels formed to mimic the two lowest frequency harmonic tones within the boatwhistle. Candidate boatwhistle calls are identified based on the correlation between these kernels and a low-frequency spectrogram of the data. Next, frequency-reassigned spectrogram images of these candidates are formed and input into the pre-trained ResNet-50 convolutional neural network. Finally, the activations from a deep, fully connected layer within this network are extracted and passed to a one-vs-all support-vector-machine classifier, which separates boatwhistles from the larger set of candidate signals. This classifier model was trained and evaluated using a labeled dataset of over 20,000 candidate signals generated over diverse acoustic conditions within Pamlico Sound, North Carolina, USA. The accompanying software provides an effective and efficient tool to monitor boatwhistle calls, which may facilitate a deeper understanding of the spatial distribution, behavioral patterns, and ecological roles played by oyster toadfish.

Excitation of Acoustic Modes by Tone Harmonics of a Hole in a Jet-Driven Helmholtz Oscillator

Excitation of Acoustic Modes by Tone Harmonics of a Hole in a Jet-Driven Helmholtz Oscillator

Estimation of the Fan Rotational Speed Using Flyover Audio Recordings

Aircraft noise emissions affect societies around the world by impacting the population’s health and land use planning. This calls for simulation tools able to predict these types of noise emissions with high accuracy. A crucial aircraft parameter to achieve satisfying precision is the rotating frequency of the low-pressure shaft of the turbofan engine, called N1. N1 determines the engine’s power use and is here estimated acoustically from ground-based microphones. A new method for dynamic N1 estimation is presented, which is more robust as compared to earlier approaches. It makes use of different aircraft sound characteristics and combines two methods. The first method tracks multiple fan tone harmonics over time within a de-Dopplerized sound pressure spectrogram. This frequency-tracking task is solved by dynamic programming to find the global optimum. The second method relates to buzz-saw noise, and is thus applied to departures only. The buzz-saw fundamental frequency is estimated in the cepstral domain. Both submethods are separately validated and assessed with concurrent sound pressure measurements and flight deck recording data of N1. The new robust N1 estimation method will be applied in noise measurement campaigns with the goal of improving current aircraft noise emission models.

Excitation of Acoustic Modes by Tone Harmonics of a Hole in a Jet-Driven Helmholtz Oscillator

Periodic pressure fluctuations were studied experimentally in the model of a jet-driven Helmholtz oscillator with a cylindrical chamber with a round air jet impinging on the sharp edge of the outlet. The evolution of the amplitude–frequency spectrum of the hole tone from its appearance at a jet velocity of about 2 m/s to excitation of the first acoustic resonance mode at the Helmholtz frequency was studied. The hole tone was a family of harmonics that progressively became more complex as the length and velocity of the jet increased. The successive occurrence of a family of acoustic modes on the harmonics of the jet tone with a further increase in jet velocity is studied. Modes at the Helmholtz frequency arose alternately on the harmonics of the hole tone in the gain band of the oscillator, starting from the highest harmonic. The first mode occurred at the highest harmonic; the second mode, at the previous harmonic; and so on. The final mode arose at the fundamental harmonic of the hole tone and had the maximum amplitude. With a further increase in the Reynolds number, periodic pressure fluctuations became disordered turbulent fluctuations. With a sufficient chamber size and jet velocity, azimuthal and half-wave resonances appeared at the highest harmonic of the hole tone. The largest Reynolds number at which resonance at the Helmholtz frequency was observed was 105.

Counterpoint and Non-harmonic tone Arrangements on “Bungong Jeumpa” Song Arrangements Works of Paul Widyawan

The purpose of this study is to analyze and describe Paul Widyawan's “Bungong Jeumpa” song about conterpoint and non-harmonic tone arrangements. This type of research is qualitative with a content analysis approach, namely: objectivity, systematic, and generalization. The data in this study were taken from literature studies and song scores. The analysis technique uses choral composition techniques, conterpoint, and non-harmonic tones. The results showed that the composition of “Bungong Jeumpa”'s song has three parts, namely: intro, content, and coda. The intro consists of 8 measure chambers, contains 20-measure chambers, and 4 coda chambers. The arrangement of the song is a polyphony-homophony texture, based on the Cantus Firmus. SATB's melodic contour relationships are tonal conterpoint in the key of A minor harmonics. Each melodic contour moves with the same rhythm and is generally different. Differences in melodic contours produce four types of Motus, namely parallellus, contrarius, obliqus, and rectus. Besides that, with the differences in the rhythm and melody of the songs on SATB with the presence of insert notes between the harmonic tones, there is also a different musical atmosphere. Based on position, motion, and solutions of dissonant tones, five types were found, namely: passing tone, appoggiatura, changing tone, neighbouring tone, and retardation.

Mechanisms of masking by Schroeder-phase harmonic tone complexes in the budgerigar (Melopsittacus undulatus)

Schroeder-phase harmonic tone complexes can have a flat temporal envelope and rising or falling instantaneous-frequency sweeps within F0 periods, depending on the phase-scaling parameter C. Human tone-detection thresholds in a concurrent Schroeder masker are 10-15 dB lower for positive C values (rising frequency sweeps) compared to negative (falling sweeps), potentially due to cochlear mechanics, though this hypothesis remains controversial. Birds provide an interesting model for studies of Schroeder masking because many species produce vocalizations containing frequency sweeps. Prior behavioral studies in birds suggest less behavioral threshold difference between maskers with opposite C values than in humans, but focused on low masker F0s and did not explore neural mechanisms. We performed behavioral Schroeder-masking experiments in budgerigars (Melopsittacus undulatus) using a wide range of masker F0 and C values. Signal frequency was 2800 Hz. Neural recordings from the midbrain characterized encoding of behavioral stimuli in awake animals. Behavioral thresholds increased with increasing masker F0 and showed minimal difference between opposite C values, consistent with prior budgerigar studies. Midbrain recordings showed prominent temporal and rate-based encoding of Schroeder F0, and in many cases, marked asymmetry in Schroeder responses between C polarities. Neural thresholds for Schroeder-masked tone detection were often based on a response decrement compared to the masker alone, consistent with prominent modulation tuning in midbrain neurons, and were generally similar between opposite C values. The results highlight the likely importance of envelope cues in Schroeder masking and show that differences in supra-threshold Schroeder responses do not necessarily result in neural threshold differences.

Teaching Fourier series with tone experiments based on smartphone applications

AbstractThis study proposes a tone experiment using multiple smartphones or tablets to assist Fourier series teaching combined with a pedagogical strategy of the Visible Thinking framework. Fourier analysis is widely applied in many fields; therefore, it is an important subject in many professional courses of colleges, especially in engineering. While Fourier analysis is the core theoretical foundation of various experimental techniques, undergraduate courses often teach Fourier analysis from a mathematical perspective, leaving students with little intuition about how Fourier analysis works. The proposed tone experiment requires teamwork for students to manipulate smartphones to synthesize harmonic tones to simulate a periodic wave so that students can intuitively understand the physical meaning of the Fourier series formula. In addition, we conducted a pedagogical study on this course to evaluate the effects. The proposed method successfully improved the learning outcomes of beginner students and reduced the anxiety associated with learning Fourier analysis. Compared with the class that did not use the proposed tone experiment, the quiz scores improved by an average of 3.77 points. The students gave positive feedback and comments on the proposed experiments and teaching methods.

The effect of rhythm on selective listening in multiple-source environments for young and older adults

Understanding continuous speech with competing background sounds is challenging, particularly for older adults. One stimulus property that may aid listeners understanding of to-be-attended (target) material is temporal regularity (rhythm). In the context of speech-in-noise understanding, McAuley and colleagues recently showed a target rhythm effect whereby recognition of target speech was better when natural speech rhythm of a target talker was intact than when it was temporally altered. The current study replicates the target rhythm effect using a synthetic vowel sequence paradigm in young adults (Experiment 1) and then uses this paradigm to investigate potential age-related changes in the effect of rhythm on recognition (Experiment 2). Listeners identified the last three vowels of temporally regular (isochronous) and irregular (anisochronous) synthetic vowel sequences in quiet and with a competing background sequence of vowel-like harmonic tone complexes presented at various tempos. The results replicated the target rhythm effect whereby temporal regularity in the vowel sequences improved identification accuracy of young listeners compared to irregular vowel sequences. The magnitude of the effect was not found to be influenced by background tempo, but faster background tempos led to greater vowel identification accuracy independent of regularity. Older listeners also demonstrated a target rhythm effect but received less benefit from the temporal regularity of the target sequences than did young listeners. This study highlights the importance of rhythm for understanding age-related differences in selective listening in complex environments and provides a novel paradigm for investigating effects of rhythm on perception.

An Optimization of Least-Square Harmonic Phasor Estimators in Presence of Multi-Interference and Harmonic Frequency Variance

The wide application of power electronic devices brings an increasing amount of undesired harmonic and interharmonic tones, and accurate harmonic phasor estimation under a complex signal input is an important task for smart grid applications. In this paper, an optimization of least-square dynamic harmonic phasor estimators, considering multi-interference and harmonic frequency variance, is proposed. A comprehensive error index (CEI) composed of the fundamental-leakage-led harmonic amplitude estimation error, harmonic mutual interference, out-of-band interference, and harmonic frequency deviation is employed. The largest CEI part of least-square algorithms using three different signal decomposition models is analyzed for the first time, and variables to reduce this error component are then introduced using singular value decomposition. With the CEI and defined variables, a minimum-error estimation of harmonic phasors under various interference and harmonic frequency change is discussed. Numerical tests are performed, and the test results show that after the proposed optimization is applied to least-square algorithms, the harmonic phasor estimation errors are considerably reduced, especially for low-order harmonics. We also show the possibility of choosing desired optimal phasor filter design by balancing the measurement accuracy and data latency. For example, when the window length is set to three nominal cycles, the proposed optimization can yield both good accuracy and fast measurement speed for estimating harmonic phasors under multi-interference and harmonic frequency variance.

Sensitivity to Frequency Modulation is Limited Centrally.

Modulations in both amplitude and frequency are prevalent in natural sounds and are critical in defining their properties. Humans are exquisitely sensitive to frequency modulation (FM) at the slow modulation rates and low carrier frequencies that are common in speech and music. This enhanced sensitivity to slow-rate and low-frequency FM has been widely believed to reflect precise, stimulus-driven phase locking to temporal fine structure in the auditory nerve. At faster modulation rates and/or higher carrier frequencies, FM is instead thought to be coded by coarser frequency-to-place mapping, where FM is converted to amplitude modulation (AM) via cochlear filtering. Here, we show that patterns of human FM perception that have classically been explained by limits in peripheral temporal coding are instead better accounted for by constraints in the central processing of fundamental frequency (F0) or pitch. We measured FM detection in male and female humans using harmonic complex tones with an F0 within the range of musical pitch but with resolved harmonic components that were all above the putative limits of temporal phase locking (>8 kHz). Listeners were more sensitive to slow than fast FM rates, even though all components were beyond the limits of phase locking. In contrast, AM sensitivity remained better at faster than slower rates, regardless of carrier frequency. These findings demonstrate that classic trends in human FM sensitivity, previously attributed to auditory nerve phase locking, may instead reflect the constraints of a unitary code that operates at a more central level of processing.SIGNIFICANCE STATEMENT Natural sounds involve dynamic frequency and amplitude fluctuations. Humans are particularly sensitive to frequency modulation (FM) at slow rates and low carrier frequencies, which are prevalent in speech and music. This sensitivity has been ascribed to encoding of stimulus temporal fine structure (TFS) via phase-locked auditory nerve activity. To test this long-standing theory, we measured FM sensitivity using complex tones with a low F0 but only high-frequency harmonics beyond the limits of phase locking. Dissociating the F0 from TFS showed that FM sensitivity is limited not by peripheral encoding of TFS but rather by central processing of F0, or pitch. The results suggest a unitary code for FM detection limited by more central constraints.

Investigating the neural correlates of the emergence of pitch using harmonic and inharmonic stimuli

The emergence of a pitch percept, referred to as the pitch onset response (POR), has predominantly been studied using transitions from noise to regular interval noise (RIN), click trains and more recently, harmonic complex tones. The POR is typically an asymmetrical change response which shows a larger response for stimuli that go from having no salient pitch to a salient pitch but not vice versa. However, the spectro-temporal differences between the pitch inducing stimulus and noise make it difficult to disentangle whether the response reflects a change in regularity or a true difference in pitch salience. The aim of this experiment is to use spectrally similar stimuli that differ in pitch salience (harmonic versus inharmonic tones) without changes in temporal regularity. We recorded EEG responses in normal-hearing participants to investigate the cortical correlates of pitch emergence in humans. We used the noise to RIN transitions as a baseline measure to replicate the asymmetry in the POR. We also used transitions from harmonic to inharmonic stimuli and vice versa to investigate if the POR asymmetry would hold for stimuli with minimal spectro-temporal differences. Results from this study will help us further understand the parameters affecting this response.

In search of the missing resolved harmonics: Neural and behavioral studies of pitch discrimination

The pitch of harmonic complex tones (HCT) plays important roles in speech and music perception and in the perceptual organization of sound. Human listeners rely primarily on the spectral pattern of harmonics individually resolved by the frequency analysis in the cochlea to derive a pitch percept. Yet, evidence for a robust neural representation of resolved harmonics in animal models has been elusive, and some species appear to rely on temporal envelope cues rather than on resolved harmonics to discriminate pitch. We performed both behavioral experiments on pitch discrimination by rabbits and single-unit recordings from the auditory nerve (AN) and inferior colliculus (IC) using HCTs with equal-amplitude harmonics in which the fundamental frequency (F0) was varied over a wide range. We found that rabbits can discriminate the pitch of HCT using the spectral pattern of resolved harmonics for F0s within the range of conspecific vocalizations. Correspondingly, many IC neurons contribute to a rate-place code for the frequencies of resolved harmonics for F0s >500 Hz, and this code is more robust to variations in stimulus level than that found in the AN. A remaining challenge is to identify the neural mechanisms underlying enhanced rate-place coding in IC. [Work supported by NIH-NIDCD DC002258.]