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Advanced human-machine interfaces require improved embedded sensors that can seamlessly interact with the user. Voice-based communication has emerged as a promising interface for next generation mobile, automotive and hands-free devices. Presented here is such an audio front-end with Voice Activity Detection (VAD) hardware targeted for low-power embedded SoCs, featuring a 512 pt FFT, programmable filters, noise floor estimator and a decision engine which has been fabricated in 32 nm CMOS. The dual-VCC, dual-frequency design allows the core datapath to scale to near-threshold voltage (NTV), where power consumption is less than 50 uW. At peak energy efficiency, the core can process audio data at 2.3 nJ/frame - a 9.4X improvement over nominal voltage conditions.