Programmer Guide/SPU Reference/ZEROCROSS

Compute zero crossing rate.

[SPU ZEROCROSS X SR XMIN TYPE OUT Y]

input	description	data type	value type	default value
X	signal vector	vector	variable
SR	sampling rate in Hz	number	constant	1
XMIN	signal amplitude threshold	number	constant	0
TYPE	type of output value (DENSITY, FREQUENCY, PERIODE, COUNT)	number (int.), string	0 (= DENSITY)
output	description	data type	value type	comment
Y	zero crossing rate converted to the selected value	number	variable

Description

In this atom the zero crossings Z of the signal X are counted and than converted to the value selected by TYPE. If XMIN=0 all zero crossings, i.e. changes of signs, are counted. If XMIN>0 the absolute signal magnitude has to exceed this value between two zero crossings. To get more exact density, frequency and periode values, also the index (position) of the first (I₁) and last (I_N) zero crossing is computed.

TYPE	Y	description
0 or DENSITY	d e n s i t y = S R ⋅ Z − 1 I N − I 1 + 1 {\displaystyle density=SR\cdot {\frac {Z-1}{I_{N}-I_{1}+1}}} $density=SR\cdot {\frac {Z-1}{I_{N}-I_{1}+1}}$	number of zero crossings per second
1 or FREQUENCY	f r e q u e n c y = d e n s i t y 2 = S R 2 ⋅ Z − 1 I N − I 1 + 1 {\displaystyle frequency={\frac {density}{2}}={\frac {SR}{2}}\cdot {\frac {Z-1}{I_{N}-I_{1}+1}}} $frequency={\frac {density}{2}}={\frac {SR}{2}}\cdot {\frac {Z-1}{I_{N}-I_{1}+1}}$	frequeny in Hz
2 or PERIODE	p e r i o d e = 2 d e n s i t y = 2 S R ⋅ I N − I 1 + 1 Z − 1 {\displaystyle periode={\frac {2}{density}}={\frac {2}{SR}}\cdot {\frac {I_{N}-I_{1}+1}{Z-1}}} $periode={\frac {2}{density}}={\frac {2}{SR}}\cdot {\frac {I_{N}-I_{1}+1}{Z-1}}$	periode duration in seconds
3 or COUNT	c o u n t = Z {\displaystyle count=Z\!} $count=Z\!$	number of zero crossings

Note: To compute density, frequency or periode, the value of Z (number of zero crossings) must be greater than 1. If Z<2 and TYPE equals DENSITY, FREQUENCY or PERIODE, Y is set to 0.

See also

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