Sailesh Chittipeddi - EEWeb

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EEWeb PULSE Conexant’s Far-Field Voice Input Processing by Sailesh Chittipeddi Think of the advantages of carrying on a telephone conversation without having to worry about where the microphone is – simply talk and some hidden technology will pick up your voice, filter out any extraneous noise and send it to the other side. Just like talking to someone in the same room. No holding a phone to your ear, no headset to wear, no microphone to stay close to. And suppose we were able to control the gadgets around us simply by talking to them. No buttons to push or remote controls to find – we simply tell them to do what we want. Truly hands-free operation. Past attempts at providing this functionality have largely failed because of the difficulty with what is termed ‘far-field voice input processing’ (FFVIP). In near-field voice input processing, where a microphone is close to the mouth of a person talking, the audio quality tends to be quite good and louder than surrounding noise. When there are disturbances, several techniques are available to distinguish the 10 EEWeb | Electrical Engineering Community near-field talker from far-away disturbances. Such techniques include using spatial differences from multiple microphones, as well as taking advantage of the level difference to distinguish the higher-level voice from the noise, then combining that with statistical algorithms to deliver a high-quality voice signal output. However, if the microphone is 12-15ft (4-5m) away, then the voice signal is part of the far-field and it can be buried in a variety of disturbances – for example, echo from nearby loudspeakers, noise from traffic or appliances, reverberation from the walls of the room, and even other voices nearby. In these cases, the voice level can be much lower than the noise sources, and in the case of sound from a loudspeaker located in the same unit as the microphone (e.g. a speakerphone) that echo can easily be 100 times louder than the desired voice signal. To deliver a clear, easily understandable voice signal from a far-field source requires a new set of advanced algorithms. Conexant’s FFVIP technology addresses the following:
Echo Cancellation To suppress the echo from a local loudspeaker by a factor of a million is extremely challenging. To address this, Conexant has developed algorithms that use advanced adaptive filters to estimate the echo and perform statistical estimation of which frequency bands contain echo and which contain the desired voice. Sophisticated control algorithms tie these together to produce a natural-sounding echo-free voice signal. Background Noise Suppression When trying to provide true FFVIP, there are a variety 1M Near Field Experience Visit www.eeweb.com PROJECT of background noises that must be eliminated. Not just stationary noise from fans and motors but also time-varying noise from passing cars, airplanes, home appliances and office machines. To eliminate background noise, Conexant has developed algorithms that analyze the spectral and temporal characteristics of the microphone signal and suppress anything that is clearly not voice without impacting real voice signals. De-Reverberation When speaking inside a room, the voice signal bounces off walls and often takes hundreds of milliseconds to die down. Normally the human auditory >5M Far Field Experience 11
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Sailesh Chittipeddi - EEWeb

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