Abstract: A fast acting noise suppression device that uses energy level (volume level) of the input signal averaged over six to twenty milliseconds as a gain control for an output amplifier. The device is implemented with a digital signal processor (DSP). Rather than using an arithmetic formula to relate input volume to gain control for the amplifier, a look up table is used, allowing precise control of the function between input volume and amplifier gain. The range of lower input volumes which are suppressed by receiving relatively less amplification can be adjusted with a manual user control. The quality of the sound output as perceived by a listener is further improved by compression of high volume inputs so that they receive relatively less amplification than medium volume inputs.

Abstract: A dynamic voice operated filtering system for aircraft applications includes an input limiter, an expander, an output limiter and a user control. The input limiter receives an input signal representing a mixed voice and noise signal and filters the input signal. The input limiter outputs an attenuated version of the input signal (INL) to the expander. The input limiter attenuates the input signal so that the signal INL received by the expander remains within the expander's dynamic range. The expander outputs a signal INX, which represents an expanded version of signal INL. The signal INX has an amplitude that is a function of the amplitude of signal INL. The expander is configured to attenuate signal INL to serve as signal INX when the signal INL has a relatively low amplitude and amplifies signal INL to serve as the signal INX when the signal INL has a relatively high amplitude. The output limiter then receives the signal INX and, in response, filters the signal INX.