Reduction of Nonlinear Distortion in Condenser Microphones Using a Simple Post-Processing Technique

TL;DR

This paper presents a simple, easily implementable post-processing method to significantly reduce nonlinear distortion in condenser microphones, including MEMS types, across various applications, improving audio fidelity.

Contribution

The paper introduces a novel, parameter-based post-processing technique that effectively reduces nonlinear distortion in condenser microphones, adaptable to various hardware implementations.

Findings

Reduces second harmonic by approximately 40 dB for harmonic signals.

Decreases second-order intermodulation products by at least 20 dB in complex signals.

Applicable across frequency and dynamic ranges of microphones.

Abstract

In this paper, we introduce a novel approach for effectively reducing nonlinear distortion in single back-plate condenser microphones, i.e., most MEMS microphones, studio recording condenser microphones, and laboratory measurement microphones. This simple post-processing technique can be easily integrated on an external hardware such as an analog circuit, microcontroller, audio codec, DSP unit, or within the ASIC chip in a case of MEMS microphones. It significantly reduces microphone distortion across its frequency and dynamic range. It relies on a single parameter, which can be derived from either the microphone's physical parameters or a straightforward measurement presented in this paper. An optimal estimate of this parameter achieves the best distortion reduction, whereas overestimating it never increases distortion beyond the original level. The technique was tested on a MEMS microphone. Our findings indicate that for harmonic excitation the proposed technique reduces the second harmonic by approximately 40 dB, leading to a significant reduction in the Total Harmonic Distortion (THD). The efficiency of the distortion reduction technique for more complex signals is demonstrated through two-tone and multitone experiments, where second-order intermodulation products are reduced by at least 20 dB.