A subband beamformer on an ultra low-power miniature DSP platform

This paper presents the design and implementation of a subband cardioid beamformer on an ultra low-power miniature DSP platform, using a 2-microphone endfire array. The subband beamformer extends the classical time-domain, narrow-band algorithm to a frequency-domain, broadband implementation, so it is suitable for general speech and audio applications. An oversampled, weighted overlap-add filterbank is used to allow wide gain and phase adjustments for low power, low group delay requirements. A subband IIR filter is proposed to overcome the non-zero bandwidth of the frequency bands, and to introduce a nearly linear phase adjustment across the bands. The subband implementation allows the flexibility of integrating the beamformer with additional algorithms at different frequency ranges. The beamformer has been implemented in real-time on Dspfactory´s Toccata platform, which has been specifically designed for ultra low-power, miniature, head-mounted audio devices. At 1.25 Volts with a 5 MIPS DSP core, the Toccata consumes only about 800 micro Watts without microphones and receivers.