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 compute 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	S R ⋅ Z − 1 I N − I 1 + 1 {\displaystyle SR\cdot {\frac {Z-1}{I_{N}-I_{1}+1}}} $SR\cdot {\frac {Z-1}{I_{N}-I_{1}+1}}$	density; number of zero crossings per second

See also

<SP-atoms>

ZEROCROSS - zerocrossing rate

Usage:

ZEROCROSS x sr xmin type

Inputs:

x	signal
sr	sampling rate in Hz
xmin	threshold	0 (default)
type	Frequency | Period)

Outputs:

y	number of zero crossings

Function:

In this atom the zero crossings per second are counted, i.e. the points where between the last counted point and the current point, there exists a value xprev >= xmin and the current value xcurr<= 0 or xprev <= xmin and the current value is xcurr >= 0.

So if xmin = 0 all zero crossings, i.e. changes of signs, are counted. If xmin > 0 the signal has to exceed a certain absolute value if another point is to be counted.