<s>
In	O
audiology	O
and	O
psychoacoustics	O
the	O
concept	O
of	O
critical	B-Application
bands	I-Application
,	O
introduced	O
by	O
Harvey	O
Fletcher	O
in	O
1933	O
and	O
refined	O
in	O
1940	O
,	O
describes	O
the	O
frequency	B-Algorithm
bandwidth	I-Algorithm
of	O
the	O
"	O
auditory	O
filter	O
"	O
created	O
by	O
the	O
cochlea	O
,	O
the	O
sense	O
organ	O
of	O
hearing	O
within	O
the	O
inner	O
ear	O
.	O
</s>
<s>
Roughly	O
,	O
the	O
critical	B-Application
band	I-Application
is	O
the	O
band	O
of	O
audio	O
frequencies	O
within	O
which	O
a	O
second	O
tone	O
will	O
interfere	O
with	O
the	O
perception	O
of	O
the	O
first	O
tone	O
by	O
auditory	O
masking	O
.	O
</s>
<s>
Psychophysiologically	O
,	O
beating	B-Application
and	O
auditory	O
roughness	O
sensations	O
can	O
be	O
linked	O
to	O
the	O
inability	O
of	O
the	O
auditory	O
frequency-analysis	O
mechanism	O
to	O
resolve	O
inputs	O
whose	O
frequency	O
difference	O
is	O
smaller	O
than	O
the	O
critical	O
bandwidth	B-Algorithm
and	O
to	O
the	O
resulting	O
irregular	O
"	O
tickling	O
"	O
of	O
the	O
mechanical	O
system	O
(	O
basilar	O
membrane	O
)	O
that	O
resonates	O
in	O
response	O
to	O
such	O
inputs	O
.	O
</s>
<s>
Critical	B-Application
bands	I-Application
are	O
also	O
closely	O
related	O
to	O
auditory	O
masking	O
phenomena	O
–	O
reduced	O
audibility	O
of	O
a	O
sound	O
signal	O
when	O
in	O
the	O
presence	O
of	O
a	O
second	O
signal	O
of	O
higher	O
intensity	O
within	O
the	O
same	O
critical	B-Application
band	I-Application
.	O
</s>
<s>
Masking	O
phenomena	O
have	O
wide	O
implications	O
,	O
ranging	O
from	O
a	O
complex	O
relationship	O
between	O
loudness	B-Algorithm
(	O
perceptual	O
frame	O
of	O
reference	O
)	O
and	O
intensity	O
(	O
physical	O
frame	O
of	O
reference	O
)	O
to	O
sound	O
compression	B-General_Concept
algorithms	I-General_Concept
.	O
</s>
<s>
In	O
particular	O
,	O
a	O
band-pass	O
filter	O
allows	O
a	O
range	O
of	O
frequencies	O
within	O
the	O
bandwidth	B-Algorithm
to	O
pass	O
through	O
while	O
stopping	O
those	O
outside	O
the	O
cut-off	O
frequencies	O
.	O
</s>
<s>
This	O
leads	O
to	O
a	O
tonotopic	O
organisation	O
of	O
the	O
sensitivity	O
to	O
frequency	O
ranges	O
along	O
the	O
membrane	O
,	O
which	O
can	O
be	O
modeled	O
as	O
being	O
an	O
array	O
of	O
overlapping	O
band-pass	O
filters	O
known	O
as	O
"	O
auditory	B-Application
filters	I-Application
"	O
.	O
</s>
<s>
The	O
auditory	B-Application
filters	I-Application
are	O
associated	O
with	O
points	O
along	O
the	O
basilar	O
membrane	O
and	O
determine	O
the	O
frequency	O
selectivity	O
of	O
the	O
cochlea	O
,	O
and	O
therefore	O
the	O
listener	O
's	O
discrimination	O
between	O
different	O
sounds	O
.	O
</s>
<s>
They	O
are	O
non-linear	O
,	O
level-dependent	O
and	O
the	O
bandwidth	B-Algorithm
decreases	O
from	O
the	O
base	O
to	O
apex	O
of	O
the	O
cochlea	O
as	O
the	O
tuning	O
on	O
the	O
basilar	O
membrane	O
changes	O
from	O
high	O
to	O
low	O
frequency	O
.	O
</s>
<s>
The	O
bandwidth	B-Algorithm
of	O
the	O
auditory	O
filter	O
is	O
called	O
the	O
critical	O
bandwidth	B-Algorithm
,	O
as	O
first	O
suggested	O
by	O
Fletcher	O
(	O
1940	O
)	O
.	O
</s>
<s>
If	O
a	O
signal	O
and	O
masker	O
are	O
presented	O
simultaneously	O
then	O
only	O
the	O
masker	O
frequencies	O
falling	O
within	O
the	O
critical	O
bandwidth	B-Algorithm
contribute	O
to	O
masking	O
of	O
the	O
signal	O
.	O
</s>
<s>
The	O
larger	O
the	O
critical	O
bandwidth	B-Algorithm
the	O
lower	O
the	O
signal-to-noise	O
ratio	O
(	O
SNR	O
)	O
and	O
the	O
more	O
the	O
signal	O
is	O
masked	O
.	O
</s>
<s>
Another	O
concept	O
associated	O
with	O
the	O
auditory	O
filter	O
is	O
the	O
equivalent	O
rectangular	O
bandwidth	B-Algorithm
(	O
ERB	O
)	O
.	O
</s>
<s>
The	O
ERB	O
shows	O
the	O
relationship	O
between	O
the	O
auditory	O
filter	O
,	O
frequency	O
,	O
and	O
the	O
critical	O
bandwidth	B-Algorithm
.	O
</s>
<s>
One	O
filter	O
type	O
used	O
to	O
model	O
the	O
auditory	B-Application
filters	I-Application
is	O
the	O
gammatone	O
filter	O
.	O
</s>
<s>
The	O
shapes	O
of	O
auditory	B-Application
filters	I-Application
are	O
found	O
by	O
analysis	O
of	O
psychoacoustic	O
tuning	O
,	O
which	O
are	O
graphs	O
that	O
show	O
a	O
subject	O
's	O
threshold	O
for	O
detection	O
of	O
a	O
tone	O
as	O
a	O
function	O
of	O
masker	O
parameters	O
.	O
</s>
<s>
The	O
notched	O
noise	O
is	O
noise	O
with	O
a	O
notch	O
around	O
the	O
frequency	O
of	O
the	O
signal	O
the	O
subject	O
is	O
trying	O
to	O
detect	O
,	O
and	O
contains	O
noise	O
within	O
a	O
certain	O
bandwidth	B-Algorithm
.	O
</s>
<s>
The	O
bandwidth	B-Algorithm
of	O
the	O
noise	O
changes	O
and	O
the	O
masked	O
thresholds	O
for	O
the	O
sinusoid	O
are	O
measured	O
.	O
</s>
<s>
To	O
get	O
a	O
true	O
representation	O
of	O
the	O
auditory	B-Application
filters	I-Application
in	O
one	O
subject	O
,	O
many	O
psychoacoustic	O
tuning	O
curves	O
need	O
to	O
be	O
calculated	O
with	O
the	O
signal	O
at	O
different	O
frequencies	O
.	O
</s>
<s>
Also	O
a	O
large	O
number	O
of	O
thresholds	O
need	O
to	O
be	O
calculated	O
because	O
the	O
auditory	B-Application
filters	I-Application
are	O
asymmetrical	O
,	O
so	O
thresholds	O
should	O
also	O
be	O
measured	O
with	O
the	O
notch	O
asymmetric	O
to	O
the	O
frequency	O
of	O
the	O
signal	O
.	O
</s>
<s>
Because	O
of	O
the	O
many	O
measurements	O
needed	O
,	O
the	O
amount	O
of	O
time	O
needed	O
to	O
find	O
the	O
shape	O
of	O
a	O
person	O
's	O
auditory	B-Application
filters	I-Application
is	O
very	O
long	O
.	O
</s>
<s>
Auditory	B-Application
filters	I-Application
are	O
closely	O
associated	O
with	O
masking	O
in	O
the	O
way	O
they	O
are	O
measured	O
and	O
also	O
the	O
way	O
they	O
work	O
in	O
the	O
auditory	O
system	O
.	O
</s>
<s>
As	O
described	O
previously	O
the	O
critical	O
bandwidth	B-Algorithm
of	O
the	O
filter	O
increases	O
in	O
size	O
with	O
increasing	O
frequency	O
,	O
along	O
with	O
this	O
the	O
filter	O
becomes	O
more	O
asymmetrical	O
with	O
increasing	O
level	O
.	O
</s>
<s>
In	O
general	O
this	O
model	O
relies	O
on	O
the	O
auditory	O
system	O
containing	O
the	O
array	O
of	O
auditory	B-Application
filters	I-Application
and	O
choosing	O
the	O
filter	O
with	O
the	O
signal	O
at	O
its	O
centre	O
or	O
with	O
the	O
best	O
SNR	O
.	O
</s>
