<s>
In	O
signal	O
processing	O
,	O
a	O
comb	B-Algorithm
filter	I-Algorithm
is	O
a	O
filter	O
implemented	O
by	O
adding	O
a	O
delayed	O
version	O
of	O
a	O
signal	O
to	O
itself	O
,	O
causing	O
constructive	O
and	O
destructive	O
interference	O
.	O
</s>
<s>
The	O
frequency	O
response	O
of	O
a	O
comb	B-Algorithm
filter	I-Algorithm
consists	O
of	O
a	O
series	O
of	O
regularly	O
spaced	O
notches	O
in	O
between	O
regularly	O
spaced	O
peaks	O
(	O
sometimes	O
called	O
teeth	O
)	O
giving	O
the	O
appearance	O
of	O
a	O
comb	O
.	O
</s>
<s>
Comb	B-Algorithm
filters	I-Algorithm
are	O
employed	O
in	O
a	O
variety	O
of	O
signal	O
processing	O
applications	O
,	O
including	O
:	O
</s>
<s>
Cascaded	O
integrator	O
–	O
comb	O
(	O
CIC	O
)	O
filters	O
,	O
commonly	O
used	O
for	O
anti-aliasing	O
during	O
interpolation	B-Algorithm
and	O
decimation	B-Algorithm
operations	O
that	O
change	O
the	O
sample	O
rate	O
of	O
a	O
discrete-time	O
system	O
.	O
</s>
<s>
2D	O
and	O
3D	O
comb	B-Algorithm
filters	I-Algorithm
implemented	O
in	O
hardware	O
(	O
and	O
occasionally	O
software	O
)	O
in	O
PAL	B-Language
and	O
NTSC	O
analog	O
television	O
decoders	O
,	O
reduce	O
artifacts	O
such	O
as	O
dot	O
crawl	O
.	O
</s>
<s>
Audio	B-Algorithm
signal	I-Algorithm
processing	I-Algorithm
,	O
including	O
delay	O
,	O
flanging	O
,	O
physical	O
modelling	O
synthesis	O
and	O
digital	O
waveguide	O
synthesis	O
.	O
</s>
<s>
If	O
the	O
delay	O
is	O
set	O
to	O
a	O
few	O
milliseconds	O
,	O
a	O
comb	B-Algorithm
filter	I-Algorithm
can	O
model	O
the	O
effect	O
of	O
acoustic	O
standing	O
waves	O
in	O
a	O
cylindrical	O
cavity	O
or	O
in	O
a	O
vibrating	O
string	O
.	O
</s>
<s>
The	O
reflected	O
sound	O
takes	O
a	O
longer	O
,	O
delayed	O
path	O
compared	O
to	O
the	O
direct	O
sound	O
,	O
and	O
a	O
comb	B-Algorithm
filter	I-Algorithm
is	O
created	O
where	O
the	O
two	O
mix	O
at	O
the	O
listener	O
.	O
</s>
<s>
Comb	B-Algorithm
filters	I-Algorithm
exist	O
in	O
two	O
forms	O
,	O
feedforward	O
and	O
feedback	O
;	O
which	O
refer	O
to	O
the	O
direction	O
in	O
which	O
signals	O
are	O
delayed	O
before	O
they	O
are	O
added	O
to	O
the	O
input	O
.	O
</s>
<s>
Comb	B-Algorithm
filters	I-Algorithm
may	O
be	O
implemented	O
in	O
discrete	O
time	O
or	O
continuous	O
time	O
forms	O
which	O
are	O
very	O
similar	O
.	O
</s>
<s>
The	O
general	O
structure	O
of	O
a	O
feedforward	O
comb	B-Algorithm
filter	I-Algorithm
is	O
described	O
by	O
the	O
difference	O
equation	O
:	O
</s>
<s>
Therefore	O
,	O
for	O
the	O
feedforward	O
comb	B-Algorithm
filter	I-Algorithm
:	O
</s>
<s>
In	O
the	O
case	O
of	O
the	O
feedforward	O
comb	B-Algorithm
filter	I-Algorithm
,	O
this	O
is	O
:	O
</s>
<s>
Hence	O
the	O
magnitude	O
response	O
of	O
the	O
comb	B-Algorithm
filter	I-Algorithm
is	O
periodic	O
.	O
</s>
<s>
The	O
feedforward	O
comb	B-Algorithm
filter	I-Algorithm
is	O
one	O
of	O
the	O
simplest	O
finite	O
impulse	O
response	O
filters	O
.	O
</s>
<s>
Looking	O
again	O
at	O
the	O
-domain	O
transfer	O
function	O
of	O
the	O
feedforward	O
comb	B-Algorithm
filter	I-Algorithm
:	O
</s>
<s>
This	O
leads	O
to	O
a	O
pole	B-Algorithm
–	I-Algorithm
zero	I-Algorithm
plot	I-Algorithm
like	O
the	O
ones	O
shown	O
.	O
</s>
<s>
Similarly	O
,	O
the	O
general	O
structure	O
of	O
a	O
feedback	O
comb	B-Algorithm
filter	I-Algorithm
is	O
described	O
by	O
the	O
difference	O
equation	O
:	O
</s>
<s>
Substituting	O
into	O
the	O
-domain	O
expression	O
for	O
the	O
feedback	O
comb	B-Algorithm
filter	I-Algorithm
:	O
</s>
<s>
The	O
feedback	O
comb	B-Algorithm
filter	I-Algorithm
has	O
some	O
properties	O
in	O
common	O
with	O
the	O
feedforward	O
form	O
:	O
</s>
<s>
The	O
feedback	O
comb	B-Algorithm
filter	I-Algorithm
is	O
a	O
simple	O
type	O
of	O
infinite	O
impulse	O
response	O
filter	O
.	O
</s>
<s>
Looking	O
again	O
at	O
the	O
-domain	O
transfer	O
function	O
of	O
the	O
feedback	O
comb	B-Algorithm
filter	I-Algorithm
:	O
</s>
<s>
This	O
leads	O
to	O
a	O
pole	B-Algorithm
–	I-Algorithm
zero	I-Algorithm
plot	I-Algorithm
like	O
the	O
ones	O
shown	O
below	O
.	O
</s>
<s>
Comb	B-Algorithm
filters	I-Algorithm
may	O
also	O
be	O
implemented	O
in	O
continuous	O
time	O
.	O
</s>
