<s>
an	O
audio	O
compression	O
method	O
used	O
on	O
the	O
SPC700	O
sound	O
coprocessor	O
used	O
in	O
the	O
SNES	B-Application
,	O
as	O
well	O
as	O
the	O
audio	O
processors	O
of	O
the	O
Philips	B-Device
CD-i	I-Device
,	O
the	O
PlayStation	B-Device
,	O
and	O
the	O
Apple	O
Macintosh	B-Device
Quadra	I-Device
series	O
.	O
</s>
<s>
The	O
method	O
is	O
a	O
form	O
of	O
ADPCM	B-Algorithm
.	O
</s>
<s>
BRR	O
compresses	O
each	O
consecutive	O
sequence	O
of	O
sixteen	O
16-bit	O
PCM	B-Algorithm
samples	O
into	O
a	O
block	O
of	O
9	O
bytes	B-Application
.	O
</s>
<s>
From	O
most	O
to	O
least	O
significant	O
,	O
the	O
first	O
byte	B-Application
of	O
each	O
block	O
consists	O
of	O
four	O
bits	O
indicating	O
the	O
range	O
of	O
the	O
block	O
(	O
see	O
below	O
)	O
which	O
controls	O
the	O
size	O
of	O
steps	O
between	O
the	O
16	O
possible	O
values	O
such	O
that	O
minute	O
changes	O
can	O
be	O
recorded	O
if	O
the	O
16	O
values	O
are	O
closer	O
together	O
but	O
minute	O
changes	O
are	O
lost	O
if	O
the	O
16	O
values	O
are	O
far	O
apart	O
,	O
two	O
bits	O
indicating	O
the	O
filter	O
(	O
see	O
below	O
)	O
,	O
and	O
two	O
bits	O
of	O
control	O
information	O
for	O
the	O
SPC700	O
.	O
</s>
<s>
The	O
remaining	O
eight	O
bytes	B-Application
consist	O
of	O
16	O
signed	O
4-bit	O
nibbles	O
which	O
correspond	O
to	O
the	O
16	O
samples	O
,	O
packed	O
in	O
a	O
big-endian	O
manner	O
.	O
</s>
<s>
As	O
32	O
bytes	B-Application
of	O
input	O
become	O
9	O
bytes	B-Application
of	O
output	O
,	O
the	O
BRR	O
algorithm	O
yields	O
a	O
3.56:1	O
compression	O
ratio	O
.	O
</s>
<s>
A	O
nibble	O
n	O
in	O
a	O
block	O
with	O
filter	O
and	O
range	O
should	O
be	O
decoded	O
into	O
a	O
PCM	B-Algorithm
sample	O
using	O
the	O
following	O
second-order	O
linear	O
prediction	O
equation	O
:	O
</s>
<s>
Here	O
,	O
and	O
are	O
the	O
last-output	O
and	O
next-to-last-output	O
PCM	B-Algorithm
samples	O
,	O
respectively	O
.	O
</s>
<s>
The	O
PlayStation	B-Device
APU	O
and	O
the	O
Philips	B-Device
CD-i	I-Device
CDIC	O
add	O
another	O
set	O
of	O
coefficients	O
to	O
the	O
above	O
and	O
reorders	O
them	O
,	O
for	O
five	O
unique	O
of	O
8	O
filters	O
total	O
(	O
these	O
come	O
from	O
the	O
Green	B-Device
Book	I-Device
and	O
Yellow	B-Device
Book	I-Device
specifications	O
)	O
:	O
</s>
