An FPGA-based adaptive tuning control for a cochlea-mimicking filter channel

This paper presents the design and experimental results of an FPGA-based cochlea filter tuning control block that emulates the active nonlinear behaviour of outer hair cells (OHC) in the cochlea. The tuning block uses data measured from physiological experiments which are mapped into adaptive voltage bias of a CMOS cochlea-mimicking filter channel to tune it. It extracts signal level from inputs to the cochlea channel and feedforwards the corresponding voltage bias to the tuning stage of the filter channel. A level-dependent control of the filter gain and quality factor was observed in the measurement results. The tuning control block nonlinearly compressed wide range of audio input distinctively into about 20 dB, which is the active gain inherent in the sample cochlea channel used. Based on this work, we will be able to build an intelligent audio front-end for future machine hearing systems that is able to adaptively process sound and cope with wide dynamic sound input like the cochlea does.