Experimental evaluation of an active speech control method

We experimentally evaluated an active speech control scheme which reduces unnecessary speech radiated into the surrounding space. The intended application of this system, typically cellular phones, does not require speech to be radiated into the surrounding space, but only into the microphone. We previously proposed to reduce speech by generating phase-inverted predicted speech from a secondary loudspeaker. We used LPC recursively to predict samples ahead of the associated processing delay, which could go up to a few milliseconds. First, predicted samples of recorded speech were prepared off line. Then, both the original and the phase-inverted predicted samples were played out simultaneously from two loud speakers. It was found that: 1) speech cancellation of 10 dB is possible, but is highly speaker dependent; 2) the secondary loudspeaker should be oriented in the same direction as the primary source, i.e., the mouth for maximum cancellation.