<s>
The	O
zero-crossing	B-Algorithm
rate	I-Algorithm
(	O
ZCR	B-Algorithm
)	O
is	O
the	O
rate	O
at	O
which	O
a	O
signal	O
changes	O
from	O
positive	O
to	O
zero	O
to	O
negative	O
or	O
from	O
negative	O
to	O
zero	O
to	O
positive	O
.	O
</s>
<s>
Its	O
value	O
has	O
been	O
widely	O
used	O
in	O
both	O
speech	B-Application
recognition	I-Application
and	O
music	B-Application
information	I-Application
retrieval	I-Application
,	O
being	O
a	O
key	O
feature	O
to	O
classify	O
percussive	O
sounds	O
.	O
</s>
<s>
In	O
some	O
cases	O
only	O
the	O
"	O
positive-going	O
"	O
or	O
"	O
negative-going	O
"	O
crossings	O
are	O
counted	O
,	O
rather	O
than	O
all	O
the	O
crossings	O
,	O
since	O
between	O
a	O
pair	O
of	O
adjacent	O
positive	O
zero-crossings	B-Algorithm
there	O
must	O
be	O
a	O
single	O
negative	O
zero-crossing	B-Algorithm
.	O
</s>
<s>
For	O
monophonic	O
tonal	O
signals	O
,	O
the	O
zero-crossing	B-Algorithm
rate	I-Algorithm
can	O
be	O
used	O
as	O
a	O
primitive	O
pitch	O
detection	O
algorithm	O
.	O
</s>
<s>
Zero	B-Algorithm
crossing	I-Algorithm
rates	I-Algorithm
are	O
also	O
used	O
for	O
Voice	B-General_Concept
activity	I-General_Concept
detection	I-General_Concept
(	O
VAD	O
)	O
,	O
which	O
determines	O
whether	O
human	O
speech	O
is	O
present	O
in	O
an	O
audio	O
segment	O
or	O
not	O
.	O
</s>
