Signal processing systems

An electronic device for detecting a tap on an object having at least one acoustic/vibration sensor, configured to determine a threshold for declaring a detected tap, wherein the electronic device comprises a processor, working memory, program memory, and a communications interface, the program memory storing processor control code to:

• capture tap data comprising a digitised waveform of a tap on said object captured by said at least one acoustic/vibration sensor;
• process said captured tap data by applying a probabilistic tap detection procedure to generate time series tap metric data comprising data providing a detection metric of a potential said tap at a succession of times, wherein said time series tap metric data comprises a time series of tap detection probabilities;
• provide said time series of tap detection probabilities to a classifier for classifying said detection probabilities of potential said taps to declare one or more detected taps;
• determine a threshold for said classifier, wherein said threshold comprises a probability threshold to apply to said tap detection probabilities from said probabilistic tap detection procedure to declare a detected tap;
• and
• apply said classifier to said time series of tap detection probabilities data to declare a detected said tap on said object;
• and
• wherein to determine of said probability threshold for said classifier the electronic device is further configured to:
• identify a region of background noise in said captured tap data without taps;
• add to this background noise one or more examples of stored clean taps at one or more time locations in said background noise to generate synthetic training data;
• apply said probabilistic tap detection procedure to said generated synthetic training data comprising said one or more examples of stored clean taps in said background noise without taps, to generate training probability data;
• and
• use said training probability data to determine said threshold for said classifier.