<s>
In	O
signal	O
processing	O
,	O
a	O
quadrature	B-Algorithm
filter	I-Algorithm
is	O
the	O
analytic	O
representation	O
of	O
the	O
impulse	O
response	O
of	O
a	O
real-valued	O
filter	O
:	O
</s>
<s>
An	O
ideal	O
quadrature	B-Algorithm
filter	I-Algorithm
cannot	O
have	O
a	O
finite	O
support	O
.	O
</s>
<s>
It	O
has	O
single	O
sided	O
support	O
,	O
but	O
by	O
choosing	O
the	O
(	O
analog	O
)	O
function	O
carefully	O
,	O
it	O
is	O
possible	O
to	O
design	O
quadrature	B-Algorithm
filters	I-Algorithm
which	O
are	O
localized	O
such	O
that	O
they	O
can	O
be	O
approximated	O
by	O
means	O
of	O
functions	O
of	O
finite	O
support	O
.	O
</s>
<s>
For	O
single	O
frequency	O
signals	O
(	O
in	O
practice	O
narrow	O
bandwidth	O
signals	O
)	O
with	O
frequency	O
the	O
magnitude	O
of	O
the	O
response	O
of	O
a	O
quadrature	B-Algorithm
filter	I-Algorithm
equals	O
the	O
signal	O
's	O
amplitude	O
A	O
times	O
the	O
frequency	O
function	O
of	O
the	O
filter	O
at	O
frequency	O
.	O
</s>
