An Analog Integrated-Circuit Vocal Tract

We present the first experimental integrated-circuit vocal tract by mapping fluid volume velocity to current, fluid pressure to voltage, and linear and nonlinear mechanical impedances to linear and nonlinear electrical impedances. The 275 $\mu{\rm W}$ analog vocal tract chip includes a 16-stage cascade of two-port $\pi$-elements that forms a tunable transmission line, electronically variable impedances, and a current source as the glottal source. A nonlinear resistor models laminar and turbulent flow in the vocal tract. The measured SNR at the output of the analog vocal tract is 64, 66, and 63 dB for the first three formant resonances of a vocal tract with uniform cross-sectional area. The analog vocal tract can be used with auditory processors in a feedback speech locked loop—analogous to a phase locked loop—to implement speech recognition that is potentially robust in noise. Our use of a physiological model of the human vocal tract enables the analog vocal tract chip to synthesize speech signals of interest, using articulatory parameters that are intrinsically compact and linearly interpolatable.