# Corpus-Based Insights into Mandarin Neutral Tone: Effects of Tonal Context and Structural Patterns in Spontaneous Speech

Jingyi Sun, Nicolas Audibert, Yaru Wu, Martine Adda-Decker

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Jingyi Sun, Nicolas Audibert, Yaru Wu, Martine Adda-Decker. Corpus-Based Insights into Mandarin Neutral Tone: Effects of Tonal Context and Structural Patterns in Spontaneous Speech. 26th edition of the Interspeech Conference: Fair and Inclusive Speech Science and Technology (Interspeech 2025), International Speech Communication Association (ISCA), Aug 2025, Rotterdam, Netherlands. pp.4178-4182, 10.21437/Interspeech.2025-960. hal-05093006

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# Corpus-Based Insights into Mandarin Neutral Tone: Effects of Tonal Context and Structural Patterns in Spontaneous Speech

Jingyi Sun¹, Nicolas Audibert¹, Yaru Wu¹,²,³, Martine Adda-Decker¹,³

¹Laboratoire de Phonétique et Phonologie, CNRS & Sorbonne Nouvelle, France

²CRISCO/UR4255, CNRS & Université de Caen Normandie, France

³Laboratoire Interdisciplinaire des Sciences du Numérique, CNRS & Université Paris-Saclay, France

jingyi.sun@sorbonne-nouvelle.fr, nicolas.audibert@sorbonne-nouvelle.fr, yaru.wu@unicaen.fr, martine.adda-decker@sorbonne-nouvelle.fr

## Abstract

<figure><img src="image_2.png" /><figcaption>Figure 1: Illustration of the F0 contours of the four citation tones in Mandarin Chinese.</figcaption></figure>

This study examines the realization of Mandarin neutral tone (NT) in spontaneous conversational speech. Drawing on 8,550 phrase-medial NT tokens surrounded by citation tones, we investigate whether robust coarticulatory influences from adjacent tones persist in natural discourse and compare two subtypes of NT—one with a nasal offset and one without—thereby testing the combined effects of syllable structure and grammatical function. Our analysis confirms that adjacent tones exert a dominant influence on NT realization: ultrashort NT syllables largely continue the preceding tone's contour, while normal-to-long-duration syllables exhibit clearer transitions toward the subsequent tone. NT with a nasal offset maintains a higher pitch and greater F0 dynamics while remaining stable across durations, likely link to its stronger prosodic and grammatical cues. These findings highlight the interplay of tonal coarticulation, duration, and structural patterns in shaping NT variation.

**Index Terms:** neutral tone, spontaneous speech, corpus phonetics, Mandarin Chinese

## 1. Introduction

The lexical tonal system of Standard Mandarin Chinese consists of four citation tones (hereafter CT), which exhibit relatively fixed pitch contours and values, with predictable and stable tone sandhi patterns in connected speech. Figure 1 presents their canonical f0 contours. In addition to CT, there exists a more variable category known as the neutral tone (hereafter NT) [1, 2]. NT has no canonical pitch contour and is generally considered underlyingly underspecified [3], yet it appears to exhibit a low pitch target [4, 5].

Previous studies have primarily examined NT variation and influencing factors using carefully controlled read speech or broadcast news corpora [6], yielding reliable findings. From a broader perspective, compared to CT, NT is characterized by weaker physiological articulation and shorter duration, approximately 45%-60% of CT duration [7]. Additionally, prosodic positions and syntactic boundaries significantly influence NT variation [8, 9]. NT syllables often exhibit segmental reduction, such as consonant voicing, monophthong centralization or deletion, and diphthong contraction [10, 11]. On a finer scale, NT pitch contours are heavily influenced by the directional changes and speed of the preceding tone; specifically, NT manifests as a falling tone after CT1, CT2, or CT4, and as a rising tone after CT3, while the predictory effects of the following tone are relatively weaker, except the assimilation when followed by CT3 [5, 12]. Moreover, NT is modulated by the interaction of duration and speech rate [9].

While studies on scripted and controlled speech have yielded valuable insights, they often diverge from patterns ob-

served in spontaneous, conversational speech [13]. For instance, CT3 remains consistently long in broadcast news but shows significantly different duration patterns in casual contexts [14]. The clarity and stylization demands of read speech can also constrain speaker variability, raising concerns about ecological validity [15]. As a result, research based solely on read speech may overestimate NT regularity. To address this, the present study extends the investigation to spontaneous speech, examining whether NT exhibits systematic variation based on adjacent tonal contours, as found in highly controlled settings.

The classic paradigm for NT pitch analysis often involves sequences of three consecutive NTs, as in 妈妈们的 ("mothers"), where the second, third, and fourth syllables carry neutral tone [16, 9, 8, 12, 5]. This design has been widely used to examine tonal downstep, with the final NT consistently exhibiting the lowest pitch. However, such triplets are rare in spontaneous speech, appearing only 27 times in our dataset, suggesting that this pattern may not reflect natural conversational usage. Despite this, NTs are often treated as a homogeneous category, overlooking distinctions in grammaticalization and syllable structure. In reality, regular NTs are primarily function words [5, 17, 18], with most classified as particles, while 们 (mən) functions as a plural suffix. These function words frequently appear in syntactic constructions that require prosodic integration, highlighting their grammatical role. Their structural and functional differences call for a finer NT classification to better capture tonal behavior in natural speech.

To this end, this study examines two major NT subtypes frequently occurring in spontaneous speech: /ə/-type and /ən/-type. The /ə/-type NTs include structural particles (的, 地, 得, /tə/), aspectual/modal particles (了 /lə/, 着 /tʃə/). The /ən/-type NTs primarily consist of the plural marker 们 (mən), which differs from the particle subgroup in syllable structure, grammatical load and the position relative to prosodic boundary. By analyzing both subtypes, we investigate whether their pitch contours exhibit systematic variation and how they interact with adjacent citation tones.

Building on this classification, the present study addresses two key research questions using a large corpus: How do adjacent tones modulate NT pitch contours in spontaneous speech, and do these patterns align with previous findings? To what extent is NT pitch variation linked to its subtype (-/ə/ vs. -/ən/)?
# 2. Method

## 2.1. Corpus

We used a subset of a previously published Mandarin conversational corpus [19], recorded in pairs of colleagues or friends engaging in semi-structured discussions on selected topics. Recordings were made in stereo using a Roland R-26 and transcribed with Whisper's large model [20]. Ethical approval was granted by CER-USN (Université Sorbonne Nouvelle) and validated by the CNRS DPO (ref. 2-24092). This study analyzes 30 fully validated speakers (17 males, 13 females), totaling approximately 20 hours of spontaneous speech.

Subsequently, we used Montreal Forced Aligner (MFA) 3.0.6 [21] to align the Mandarin speech, employing the spacy-pkuseg package [22] for automatic word segmentation. The alignment process relied on pretrained pronunciation dictionaries and acoustic models. After the initial alignment, manual corrections were made in Praat 6.4.08 [23] to fix transcription errors, followed by a second alignment and verification to ensure precise time boundaries.

## 2.2. Data Processing

The extraction of f0 values for NTs was conducted using the pre-trained FCN-993 model from the fully-convolutional network framework, which has been shown the most accurate among a selection of 8 major f0 estimation algorithms [24, 25]. Trained on a multilingual corpus spanning 7 languages including Mandarin Chinese, the FCN algorithm demonstrates particular robustness in processing tonal variations while maintaining high temporal precision. F0 trajectories were linearly interpolated and resampled to 10 equidistant points for each tone contour to neutralize articulation rate effects. Notably, both the f0 extraction and the measurement of tone duration were based solely on the NT's vowel (and nasal offset, if present), excluding the voiceless onset of the syllable. Speaker normalization was achieved through 12-semitone conversion (12×log₂ (F0/F0<sub>avg</sub>)) based on per-speaker mean f0 in voiced segments, a method validated by [26] to preserve phonemic and sociolinguistic variations while ensuring cross-speaker comparability.

We excluded creaky voice data and phrase-initial/final NT syllables. The final dataset comprised 8,550 phrase-medial NT tokens, ensuring complete tonal context preservation while minimizing prosodic interference from phrase-initial pitch surges, phrase-final downsteps, and global intonation patterns. As shown in Table 1, NTs within /ɔ/ included functional particles "的"(/tɔ/), "地"(/tɔ/), and "得"(/tɔ/), "了"(/lɔ/), "着"(/tʃɔ/), while those within /ən/ were limited to the plural marker "们"(/mən/).

<table><caption>Table 1: Distribution of Neutral Tone Tokens by Subtype and Gender</caption><thead><tr><th rowspan="2">Subtype of NT</th><th colspan="2">Gender</th><th rowspan="2">Total</th></tr><tr><th>Female</th><th>Male</th></tr></thead><tbody><tr><td>-/ɔ/</td><td>2,805</td><td>4,310</td><td>7,115</td></tr><tr><td>-/ən/</td><td>565</td><td>870</td><td>1,435</td></tr></tbody></table>

## 2.3. Statistical model

This study employs Generalized Additive Mixed Models (GAMMs) [27] to examine the dynamic pitch patterns of NT in this large-scale corpus of Mandarin spontaneous speech. GAMMs provide a flexible framework for modeling nonlinear relationships while accounting for both fixed and random effects, ensuring that phonetic and prosodic influences are captured without conflating individual speaker variation. The models were fitted using mgcv (version 1.9-1) [28] and visualized with itsadug (version 2.4) [29].

Our modeling approach integrates fixed effects for subtype (Phones), preceding and following tones (Prev.Tone, Next.Tone), NT duration, and normalized time (Time Point). Nonlinear pitch trajectories are captured through thin-plate regression splines, with factor-smooth interactions examining how pitch contours vary by subtype and tonal context. Additionally, tensor product smooths were applied to jointly model the interaction between time and duration, accounting for how tonal realization unfolds over the syllable while being influenced by overall syllable length. This interaction was further examined separately for different subtypes and tonal contexts, allowing the model to capture fine-grained variations in pitch trajectories.

At the random-effects level, a smooth interaction of time by speaker captures speaker-specific variability (Speaker), while token-level variability is modeled via a random intercept (Group.ID). To address residual autocorrelation in the sequential f0 data, we incorporated an AR(1) process with $= 0.6$, to reduce the risk of over-smoothing consecutive pitch values, yielding more reliable estimates of the model's smooth components. The model was estimated using fast restricted maximum likelihood (fREML), achieving a rank of 10069/10072, an adjusted $R^2$ of 0.974, and 97.7% deviance explained (fREML: 45116, Scale est.: 0.15882). These results underscore the robustness of our modeling strategy, demonstrating that key phonetic and tonal factors are effectively captured and that the dynamic pitch realization of neutral tones in spontaneous speech is comprehensively represented within this model.

# 3. Results

## 3.1. Variation of NT across Tonal Context

The pitch contours of NT in spontaneous speech largely align with those observed in the controlled reading corpus analyzed by [30], where prosodic position and focal prominence were strictly regulated. However, certain differences emerge. Although duration is modeled as a continuous predictor, to enable a more direct interpretation of the results the effects are analyzed by considering duration values corresponding to short (30 ms), normal (80 ms) or long (170 ms) realizations. These thresholds were chosen based on [7] (averaging 96.9 ms and 106.2 ms for read and conversational speech) and our corpus (mean = 65.79 ms, sd = 37.80 ms), which shows many very short durations (30 ms) and few above 200 ms. As Figure 2 shows, NT's pitch trajectories vary with adjacent CT and duration: at 30 ms, NT's pitch remains stable, largely retaining the preceding tone's level, while at 80 ms and 170 ms, more pronounced pitch movements occur under the influence of the preceding tone. Notably, when followed by CT3, NT consistently exhibits a significant upward pitch shift ($p < 0.05$), creating a clear tonal distinction. This pattern suggests a systematic interaction between NT and its tonal environment, where both adjacent tones and duration shape its final realization.
<figure><img src="image_3.png" /><figcaption>Figure 2: Fitted Pitch Contours of NT Across Various Preceding and Following Tone Combinations at Three Duration Conditions (Short = 30ms, Normal = 80ms, Long = 170ms), with 95% Confidence Intervals</figcaption></figure>

### 3.1.1. Foundational Constraints of Preceding Tones on NT Contours

The preceding tone (Prev.Tone) has a significant impact on NT's pitch realization. When NT follows CT1, which serves as the baseline condition, it begins at the highest pitch and, given sufficient duration, exhibits a sharp downward trajectory. In contrast, when preceded by CT2 (Prev.Tone2 = -0.61 st, *p* < 0.001) or CT4 (Prev.Tone4 = -1.28 st, *p* < 0.001), NT's initial pitch is noticeably lower, though the effect is less pronounced. The most substantial influence comes from CT3 (Prev.Tone3 = -2.28 st, *p* < 0.001), which exerts the strongest downward pull on NT's initial pitch. This aligns with the observation in Figure 2, where NT reaches its lowest starting pitch when preceded by CT3 and then gradually rises.

Crucially, when NT is extremely short (30ms), it fails to establish an independent tonal contour, instead acting as a phonetic continuation of the preceding tone. However, as duration extends to normal or long (80ms or 170ms), NT begins to develop a more distinct tonal trajectory. Specifically, when preceded by CT1/2/4, NT tends to exhibit a descending pattern, whereas CT3 leads to a low-to-high rising contour. This suggests that CT3 not only depresses NT's initial pitch but also conditions its upward movement when given sufficient time to fully manifest.

### 3.1.2. Asynchronous Modulation by Following Tones

The influence of the following tone (Next.Tone) on NT's pitch is also highly significant. In particular, when NT is followed by CT3 (Next.Tone3 = 0.86 st, *p* < 0.001), it undergoes a strong upward shift in pitch, reinforcing the distinct tonal separation observed in Figure 2. By contrast, CT2 (Next.Tone2 = 0.16 st, *p* = 0.09) and CT4 (Next.Tone4 = 0.11 st, *p* = 0.16) exhibit positive coefficients but do not reach statistical significance, suggesting a weaker effect on NT's pitch. This pattern indicates that when the upcoming syllable carries CT3, NT is systematically elevated in pitch, creating a tonal boundary between CT3 contexts and other tonal environments.

Moreover, the upward shift induced by CT3 interacts with the downward pull of preceding CT3, further reinforcing NT's characteristic low-to-high pitch trajectory when duration is sufficient. This interaction highlights the importance of both tonal adjacency and temporal factors in shaping NT's phonetic realization.

### 3.1.3. Duration-Dependent Tonal Interaction

Duration plays a crucial role in shaping NT's tonal realization, as reflected in the significant effect of the smooth term for duration (*F* = 28.0, *p* < 0.001). In extremely short duration (30ms), NT's pitch contour primarily reflects the inertia of the preceding tone, while the influence of the following tone is generally suppressed. As duration increases, NT gains more time to transition between adjacent tones, allowing the influence of both the preceding and following tones to emerge, thereby forming a more fully realized contour.

For instance, at longer duration (170ms), NT exhibits a descending trend when preceded by CT1/2/4, whereas preceding CT3 results in a characteristic low-to-high rise. Additionally, when followed by CT3, NT undergoes a further upward shift, leading to a distinct tonal separation from NT in other following tone contexts. Notably, while the influence of the following tone typically requires sufficient duration to manifest, CT3 presents an exception. Even in ultrashort NT duration (30ms), where the contour itself remains relatively simple and primarily shaped by the preceding tone, NT's pitch range is significantly elevated when followed by CT3. This suggests that the assimilatory effect of CT3 is particularly robust, overriding the typical duration-dependent pattern of tonal interaction.

These findings reveal a hierarchical NT production system: the preceding tone establishes contour trajectories, the following tone modify paths beyond critical durations, and speech style modulates the pitch range to achieve functional adaptation.
## 3.2. Variation of NT in Two Subtypes: -/ə/ and -/ən/

The overall pitch level provides a clear indication of the divergence between /ə/ and /ən/. As illustrated by Figure 3, the fitted f0 trajectories plotted across normalized time (Time Point) for three representative duration conditions (30 ms, 80 ms, and 170 ms) demonstrate that /ən/ consistently exhibits a higher pitch profile throughout its temporal course when averaged across tonal contexts. The model summary indicates that /ən/ surpasses /ə/ by 1.49 st (p < 0.001), reflecting a robust and stable difference that underscores the prominence of the plural marker in spontaneous speech.

In terms of pitch modulation over time, the smooth term comparison shown in Table 2 reveals a bit more pronounced contour shifts for /ən/, where s(Time Point):-/ə/ has an edf of 3.04 and an F-value of 2.69, whereas the corresponding term for -/ən/ shows an edf of 4.80 with an F-value of 6.71 (p < 0.001). Thus, /ən/ undergoes a more complex pitch trajectory, likely tied to its grammatical load, which requires clearer acoustic marking to signal plurality.

<table><caption>Table 2: Comparison of F0 Characteristics between -/ə/ and -/ən/</caption><thead><tr><th>Variable</th><th>Est. (β) / edf</th><th>F-Value</th></tr></thead><tbody><tr><td>Phones-/ə/ (Baseline)</td><td>Baseline</td><td>—</td></tr><tr><td>Phones-/ə/n</td><td>1.49</td><td>—</td></tr><tr><td>s(Time Point):-ə</td><td>3.04</td><td>2.69 *</td></tr><tr><td>s(Time Point):-ən</td><td>4.80</td><td>6.71 ***</td></tr><tr><td>s Duration):-ən</td><td>2.46</td><td>28.02 ***</td></tr><tr><td>ti(Time Point, Duration):-ə</td><td>39.47</td><td>5.13 ***</td></tr><tr><td>ti(Time Point, Duration):-ən</td><td>10.64</td><td>0.98</td></tr></tbody></table>

Note: Est. (β) = Estimated coefficient for parametric terms.

edf = Effective degrees of freedom for smooth terms.

*** p < 0.001, ** p < 0.01, * p < 0.05.

Regarding duration, the two-dimensional smooth term ti(Time Point, Duration) sheds further light on each subtype's propensity for reduction. Although /ən/ exhibits more dynamic f0 changes over time, it shows a non-significant time-duration interaction, suggesting that it is relatively resistant to alterations in speech rate or utterance length. In contrast, /ə/ undergoes substantial stretching or compression as utterance length varies (Table 2; edf = 39.47, F = 5.13, p < 0.001 for /ə/, but non-significant for /ən/). One likely explanation is that /ə/ experiences greater phonetic weakening and durational variability, whereas /ən/ maintains a more stable pitch contour, reinforcing its grammatical function.

These findings highlight a syntax-prosody distinction between /ə/ and /ən/ in spontaneous speech. /ə/ is more susceptible to reduction and temporal variation, aligning with prosodic economy, while /ən/ preserves stronger prosodic cues, likely serving as a robust grammatical marker. This reflects an essential syntax-prosody interaction, where /ən/ requires clearer demarcation in speech processing, while /ə/ conforms to reduction mechanisms that enhance speech fluidity.

Crucially, these prosodic patterns interact with syntactic distributions. According to the prosodic boundary hierarchy [8], SP boundaries require stronger prosodic separation, which elevates the pitch of /ən/—a plural marker typically found at higher-level boundaries—to enhance its perceptual prominence.

<figure><img src="image_4.png" /><figcaption>Figure 3: Predicted F0 Contours of NT in Mandarin: Effects of Duration and Subtypes, Averaged Across Tonal Contexts</figcaption></figure>

In contrast, /ə/, which often occurs at Modifier-Head positions or lower, faces less demand for prominence, leading to a lower pitch and faster vowel reduction [31, 32]. This interplay between syntax and acoustics shows how grammar and prosody converge to balance communicative clarity with efficient speech production.

## 4. Discussion

Our findings confirm that NT in spontaneous speech is strongly influenced by adjacent citation tones, aligning with patterns observed in earlier controlled-speech studies. This suggests a systematic interaction between NT and its tonal environment, where both neighboring tones and duration shape its final realization. Specifically, preceding tones establish the initial pitch trajectory, while following tones continue to modify the contour beyond critical durations. Additionally, stylistic speech registers globally adjust the dynamic range to enhance functional contrast. Among these effects, a particularly striking effect emerges with a preceding CT3 (low), which strongly raises NT, whereas CT1 (high), CT2 (rising), and CT4 (falling) generally produce descending NT contours. However, in casual conversation, these tonal patterns tend to be realized within a more compressed pitch range, reflecting the reduced prosodic space of spontaneous speech.

Beyond tonal coarticulation, our analyses reveal a systematic difference between NT subtypes: /ən/ consistently exhibits a higher pitch trajectory than /ə/. This difference may stem from its function as a plural marker, as seen in "[i] (/mən/)," which frequently occurs in syntactically and prosodically prominent positions. Even within a compressed prosodic framework, the elevated pitch of /ən/ suggests that certain function words retain distinct acoustic cues linked to their grammatical salience.

Taken together, these results position NT at the intersection of phonetic coarticulation and grammatical-prosodic structuring. Although NT is typically regarded as unstressed, the pitch elevation associated with /ən/ indicates that its realization can still vary according to different degrees of grammatical relevance, even in spontaneous speech, where the overall pitch range remains constrained. Future research could further explore how syntactic roles, discourse-pragmatic factors, or speaker-specific prosodic patterns influence NT production, offering deeper insights into the interaction between tonal reduction and linguistic structure in naturally occurring Mandarin speech.
## 5. Acknowledgements

The research was funded by the French National Research Agency through the DIPVAR project (ANR-21-CE38-0019), as well as by the Laboratoire d'Excellence "Empirical Foundations of Linguistics" (LabEx EFL, ANR-10-LABX-0083). Jingyi Sun is also supported by the China Scholarship Council (CSC Grant No. 202208410095).

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