Detection and removal of switching noise in push-to-talk and voice operated exchange communications systems

This paper addresses the detection and removal of key clicks in the NATO non-native Air Traffic Control database. Key clicks are impulse-like noises generated in Push-to-Talk (PTT) and Voice Operated eXchange (VOX) communications systems. The removal of key clicks can improve the quality of the signal for both listening and machine processing. The detection of key clicks could also assist in other applications, such as speech segmentation on these types of channels. The approach taken was to first apply a Recursive Least Squares (RLS) whitening filter to augment the key clicks. Outlier detection based on order statistics was then applied to detect the candidate key click samples. Finally, sample values extending to the second zero crossing prior to a detected key click and to the third zero crossing following a detected key click were set to zero to remove the key clicks. With this approach 98.3% detection of the key clicks with only 0.19% false alarms was obtained.