<s>
An	O
audio	B-Application
plug-in	I-Application
,	O
in	O
computer	O
software	O
,	O
is	O
a	O
plug-in	B-Application
that	O
can	O
add	O
or	O
enhance	O
audio-related	O
functionality	O
in	O
a	O
computer	B-Application
program	I-Application
.	O
</s>
<s>
Such	O
functionality	O
may	O
include	O
digital	B-General_Concept
signal	I-General_Concept
processing	I-General_Concept
or	O
sound	O
synthesis	O
.	O
</s>
<s>
Audio	B-Application
plug-ins	I-Application
usually	O
provide	O
their	O
own	O
user	B-Application
interface	I-Application
,	O
which	O
often	O
contains	O
GUI	O
widgets	O
that	O
can	O
be	O
used	O
to	O
control	O
and	O
visualise	O
the	O
plug-in	B-Application
'	O
s	O
audio	O
parameters	O
.	O
</s>
<s>
There	O
are	O
three	O
broad	O
classes	O
of	O
audio	B-Application
plug-in	I-Application
:	O
those	O
which	O
transform	O
existing	O
audio	O
samples	O
,	O
those	O
which	O
generate	O
new	O
audio	O
samples	O
through	O
sound	O
synthesis	O
and	O
those	O
which	O
analyze	O
existing	O
audio	O
samples	O
.	O
</s>
<s>
Although	O
all	O
plug-in	B-Application
types	O
can	O
technically	O
perform	O
audio	O
analysis	O
,	O
only	O
specific	O
formats	O
provide	O
a	O
mechanism	O
for	O
analysis	O
data	O
to	O
be	O
returned	O
to	O
the	O
host	O
.	O
</s>
<s>
The	O
program	O
used	O
to	O
dynamically	B-Operating_System
load	I-Operating_System
audio	B-Application
plug-ins	I-Application
is	O
called	O
a	O
plug-in	B-Application
host	O
.	O
</s>
<s>
Example	O
hosts	O
include	O
Bidule	B-Application
,	O
Gig	B-Operating_System
Performer	I-Operating_System
,	O
Mainstage	B-Application
,	O
REAPER	B-Application
and	O
Sonic	B-Application
Visualiser	I-Application
.	O
</s>
<s>
Plug-ins	B-Application
can	O
also	O
be	O
used	O
to	O
host	O
other	O
plug-ins	B-Application
.	O
</s>
<s>
Communication	O
between	O
host	O
and	O
plug-in(s )	O
is	O
determined	O
by	O
a	O
plug-in	B-Application
API	B-General_Concept
.	O
</s>
<s>
The	O
API	B-General_Concept
declares	O
functions	O
and	O
data	B-General_Concept
structures	I-General_Concept
that	O
the	O
plug-in	B-Application
must	O
define	O
in	O
order	O
to	O
be	O
usable	O
by	O
a	O
plug-in	B-Application
host	O
.	O
</s>
<s>
Additionally	O
,	O
a	O
functional	O
specification	O
may	O
be	O
provided	O
,	O
which	O
defines	O
how	O
the	O
plug-in	B-Application
should	O
respond	O
to	O
function	O
calls	O
,	O
and	O
how	O
the	O
host	O
should	O
expect	O
to	O
handle	O
function	O
calls	O
to	O
the	O
plug-in	B-Application
.	O
</s>
<s>
The	O
specification	O
may	O
also	O
include	O
documentation	O
about	O
the	O
meaning	O
of	O
variables	O
and	O
data	B-General_Concept
structures	I-General_Concept
declared	O
in	O
the	O
API	B-General_Concept
.	O
</s>
<s>
The	O
API	B-General_Concept
header	B-Language
files	I-Language
,	O
specification	O
,	O
shared	O
libraries	O
,	O
license	B-License
and	O
documentation	O
are	O
sometimes	O
bundled	O
together	O
in	O
an	O
SDK	B-Application
.	O
</s>
