OBJECTIVE: To investigate the relationship between auditory function and vocal fundamental frequency (F0) using binaural masking with speech noise during sustained vowel vocalization. DESIGN: Eight healthy subjects were instructed to vocalize the sustained vowel /a/ at the intensities of 65 to 75 dBA and 90 to 100 dBA as steadily as possible. The phonations without noise masking were compared with the phonations under masking with 85-dBA speech noise presented to both ears through headphones. The F0s were obtained by using autocorrelation of the voice signals and were converted to cents to form a F0 sequence. The power spectrum of the F0 sequence was then acquired using fast Fourier transformation. RESULTS: A significant increase in the power spectrum in the frequency range of <3 Hz (p < 0.05, paired Student t-test) appeared under noise masking. A negative feedback control of the auditory system on F0 is suggested regarding F0 modulations of <3 Hz. CONCLUSIONS: The auditory system helps control a stable F0 during sustained vowel production by decreasing F0 modulation at <3 Hz. Power spectral analysis of F0 may be used to assess the interaction between F0 production and auditory feedback.