The AFWERX team has been engaged by the USAF to find sources for a redesign of the current Fixed Wing helmet for it’s next generation. VOCAL has accepted the challenge, and will apply it’s expertise in audio engineering to design and implement a communication path that gets through the audio you want, but not the noise you don’t.
Executive Summary: The new helmet design should include means to improve pilot voice communication. The noisy acoustic cockpit environment makes communication difficult. Through the use of digital signal processing and voice quality enhancement (VQE), the intelligibility and integrity of voice communication can be improved. This eases the pilot’s effort to relay and/or receive critical commands. Our VQE functions can be tailored to work with two or more microphones and support low power embedded processors.
Idea Description: VOCAL proposes the utilization of Dual Microphone Adaptive Noise Reduction (ANR) and Post Process Noise Reduction (PPNR) software as a front-end to helmet communication systems. VOCAL’s Dual Microphone ANR implementation is an adaptive identification filtering system, very similar to line and acoustic echo cancellation. As shown in the below figure, the noisy speech microphone signal, Y1(N) contains a desired signal, a linear-transformed copy of the noise source, and Y2(N) contains a reference of the noise source signal. An adaptive filter will be used to find the optimal filter which will minimize the output power of E(N). Resulting in the cancellation of the background noise while preserving the desired speech.
The PPNR software takes the signal channel output from the ANR software and further enhances the speech quality of the noisy microphone by estimating the noise spectrum in the frequency domain and applying a frequency dependent gain function.
Value Statement: Use of multiple microphones for voice quality enhancements has well established benefits. Signal to noise ratio (SNR) improvement can be greater than 20dB. When a second microphone provides a noise sample of the acoustic environment, the ANR algorithm adaptively tracks and cancels non-stationary noise sources allowing for a maintained speech quality throughout the pilot’s flight. These algorithms have already been developed and successfully implemented in other high noise communication systems.