The zero-crossing rate is the rate of sign-changes along a signal, i.e., the rate at which the signal changes from positive to negative or back. This feature has been used heavily in both speech recognition and music information retrieval, being a key feature to classify percussive sounds.
ZCR is defined formally as
where is a signal of length and is an indicator function.
In some cases only the "positive-going" or "negative-going" crossings are counted, rather than all the crossings - since, logically, between a pair of adjacent positive zero-crossings there must be one and only one negative zero-crossing.
Zero crossing rates are used for Voice activity detection (VAD), i.e., finding whether human speech is present in an audio segment or not.
- * Chen, C. H., Signal processing handbook, Dekker, New York, 1988
- Gouyon F., Pachet F., Delerue O. (2000),Classifying percussive sounds: a matter of zero-crossing rate?, in Proceedings of the COST G-6 Conference on Digital Audio Effects (DAFX-00), Verona, Italy, December 7–9, 2000. Accessed 26 April 2011.
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