Comparison Of Subglottal-coupling And Interdental-space Effects On Formant Transitions

In phonetics,according to the tongue position in pronunciation,vowels can be divided into front vowel and back vowel.Researchers found that,during the pronunciation from front vowel to back vowel,a second formant discontinuity has been observed in the speech spectrogram.In the further analysis of this discontinuity phenomenon,the MIT speech group considered that it was because of the acoustic coupling arose by the interaction between vocal tract(VT)above the glottis and the trachea below the glottis,which introduces a stationary anti-resonance,the second subglottal formant(SgF2),into vocal tract transfer function.And a result of this effect is that asecond formant(F2)discontinuity occurs near this anti-resonance occasionally,with a second formant(F2)amplitude attenuation(A2).However,other researchers found another possible reason for this F2 discontinuity,which is called the interdental space effect.It is because of the space between upper and lower dental arches change in volum thus arising an area change of oral cavity.The interdental spaces form a bilateral side branches thus introducing a moving anti-resonance into vocal tract transfer function and across the F2 and F3,then separates them and causes an F2 discontinuity and F3 discontinuity.As the second formant discontinuity is considered to be caused by two possible reasons,the subglottal coupling effect and interdental space effect.Previous researches about these two effects are all based on English,so this article analyzes the two effects on Chinese mandarin with various changes of tones.We explore whether the second formant discontinuity also occurs near SgF2 during the transition between front and back vowels.Besides,previous researchers did not define the boundary of these two effects.Then,how to distinctive the two effects and which effect contributes more to the second formant discontinuity are what we need to discuss and analyze.In this article,we use microphone to record the speech signal when Chinese speakers articulate particular Chinese text.At the same time,a vibration sensor is used to record the vibration signal of the trachea.These two kinds of signals are used to explore the F2 discontinuity.In the exploration,we found that F2 discontinuity occurs near SgF2 during the transition from back vowel to front vowel,which supports the subglottal coupling effect(SCE).Furthermore,an F3 discontinuity is also found to occur but has a time lag with F2 discontinuity.This is a support for interdental space effect(ISE).At the same time,according to the statistical analysis,we found that the interdental space effect occurs with a larger possibility.