Zero Crossing Rate

Zero-crossing rate (ZCR) is another basic acoustic feature that can be computed easily. It is equal to the number of zero-crossing of the waveform within a given frame. ZCR has the following characteristics:

• ZCR of unvoiced sounds and environmental noise are usually larger than voiced sounds, which has observable fundamental periods.
• It is hard to distinguish unvoiced sounds from environmental noise by using ZCR alone since they have similar ZCR values.
• ZCR is often used in conjunction with energy (or volume) for end-point detection. In particular, ZCR is used for detecting the start and end positions of unvoiced sounds.
• Some people use ZCR for rough fundamental frequency estimation, but it is highly unreliable unless further refine procedure is taken for post-processing.