<s>
Echo	B-Algorithm
removal	I-Algorithm
is	O
the	O
process	O
of	O
removing	O
echo	B-Protocol
and	O
reverberation	O
artifacts	O
from	O
audio	O
signals	O
.	O
</s>
<s>
The	O
reverberation	O
is	O
typically	O
modeled	O
as	O
the	O
convolution	B-Language
of	O
a	O
(	O
sometimes	O
time-varying	O
)	O
impulse	O
response	O
with	O
a	O
hypothetical	O
clean	O
input	O
signal	O
,	O
where	O
both	O
the	O
clean	O
input	O
signal	O
(	O
which	O
is	O
to	O
be	O
recovered	O
)	O
and	O
the	O
impulse	O
response	O
are	O
unknown	O
.	O
</s>
<s>
In	O
almost	O
all	O
cases	O
,	O
there	O
is	O
insufficient	O
information	O
in	O
the	O
input	O
signal	O
to	O
uniquely	O
determine	O
a	O
plausible	O
original	O
image	O
,	O
making	O
it	O
an	O
ill-posed	B-Algorithm
problem	I-Algorithm
.	O
</s>
<s>
This	O
problem	O
is	O
analogous	O
to	O
deblurring	B-Algorithm
in	O
the	O
image	O
processing	O
domain	O
.	O
</s>
