Zero-crossing rate

The zero-crossing rate (ZCR) is the rate at which a signal changes from positive to zero to negative or from negative to zero to positive.^[1] Its value has been widely used in both speech recognition and music information retrieval, being a key feature to classify percussive sounds.^[2]

ZCR is defined formally as

${\displaystyle zcr={\frac {1}{T-1}}\sum _{t=1}^{T-1}\left|\mathrm {sgn} [s(t)]-\mathrm {sgn} [s(t-1)]\right|}$

where ${\displaystyle s}$ is a signal of length ${\displaystyle T}$ and ${\displaystyle \mathrm {sgn} (x)}$ is a sign function defined as:

${\displaystyle \mathrm {sgn} (x)={\begin{cases}1,\quad x\geq 0\\0,\quad x<0\end{cases}}}$

In some cases only the "positive-going" or "negative-going" crossings are counted, rather than all the crossings, since between a pair of adjacent positive zero-crossings there must be a single negative zero-crossing.

For monophonic tonal signals, the zero-crossing rate can be used as a primitive pitch detection algorithm. Zero crossing rates are also used for Voice activity detection (VAD), which determines whether human speech is present in an audio segment or not.

See also

• Zero crossing
• Digital signal processing