OBJECTIVE: To investigate how resonance manipulation in Chinese vocal performance causally affects the perceived emotional valence, using an integrated two-phase approach that combines acoustic characterization with perceptual evaluation. METHODS: In the Stimulus Selection Phase, 120 native Chinese-speaking participants rated the emotional valence of 300 Chinese music excerpts (children's songs, pop, folk, operas, religious music, and modern folk-pop) on a 7-point Likert scale. Excerpts were temporally degraded to isolate melodic content. Valence scores were binned into 7 levels, and 10 excerpts per level (70 total) were re-recorded by two professional female vocalists in "full" and "thin" resonance conditions. In the perceptual evaluation phase, 80 additional participants rated the emotional valence of these recorded excerpts (280 trials) using a Latin square design. Acoustic parameters, i.e., H1-H2, mean formant bandwidth (MFB), singing power ratio (SPR), and harmonics-to-noise ratio (HNR), were analyzed, and linear regression models assessed the effects of valence level, resonance condition and their interaction on emotional ratings. RESULTS: Acoustic analyses confirmed significant differences between resonance conditions, with "full" resonance showing higher H1-H2, HNR, MFB and SPR, indicating distinct timbral qualities. Perceptual ratings revealed that valence level and resonance condition both significantly predicted emotional ratings (p < 0.001). "Full" resonance enhanced positive valence ratings and "thin" resonance reduced positive valence ratings across levels, particularly for emotionally ambiguous stimuli. CONCLUSION: Vocal resonance manipulation is a potent causal factor in shaping emotional perception in singing. The findings bridge the gap between pedagogical concepts and measurable acoustics, showing how the "full-thin" resonance continuum serves as a nuanced tool for emotional communication within the Chinese vocal tradition. These results indicate the importance of considering both acoustic implementation and perceptual outcome in understanding timbre-emotion relationships.