Modifications on NIST MarkIII array to improve coherence properties among input signals

This work describes an activity that led to the realization of a modified NIST Microphone Array MarkIII. This system is able to acquire 64 synchronous audio signals at 44.1 kHz and is primarily conceived for far-field automatic speech recognition, speaker localization and in general for hands-free voice message acquisition and enhancement. Preliminary experiments conducted on the original array had showed that coherence among a generic pair of signals was affected by a bias due to common mode electrical noise, which turned out to be detrimental for time delay estimation techniques applied to co-phase signals or to localize speakers. A hardware intervention was realized to remove each internal noise source from analog modules of the device. The modified array provides a quality of input signals that fits results expected by theory.