<s>
Differential	B-General_Concept
pulse-code	I-General_Concept
modulation	I-General_Concept
(	O
DPCM	B-General_Concept
)	O
is	O
a	O
signal	O
encoder	O
that	O
uses	O
the	O
baseline	O
of	O
pulse-code	B-Algorithm
modulation	I-Algorithm
(	O
PCM	B-Algorithm
)	O
but	O
adds	O
some	O
functionalities	O
based	O
on	O
the	O
prediction	O
of	O
the	O
samples	O
of	O
the	O
signal	O
.	O
</s>
<s>
If	O
the	O
input	O
is	O
a	O
continuous-time	O
analog	O
signal	O
,	O
it	O
needs	O
to	O
be	O
sampled	B-Algorithm
first	O
so	O
that	O
a	O
discrete-time	O
signal	O
is	O
the	O
input	O
to	O
the	O
DPCM	B-General_Concept
encoder	O
.	O
</s>
<s>
Option	O
1	O
:	O
take	O
the	O
values	O
of	O
two	O
consecutive	O
samples	O
;	O
if	O
they	O
are	O
analog	O
samples	O
,	O
quantize	B-Algorithm
them	O
;	O
calculate	O
the	O
difference	O
between	O
the	O
first	O
one	O
and	O
the	O
next	O
;	O
the	O
output	O
is	O
the	O
difference	O
.	O
</s>
<s>
Applying	O
one	O
of	O
these	O
two	O
processes	O
,	O
short-term	O
redundancy	O
(	O
positive	O
correlation	O
of	O
nearby	O
values	O
)	O
of	O
the	O
signal	O
is	O
eliminated	O
;	O
compression	O
ratios	O
on	O
the	O
order	O
of	O
2	O
to	O
4	O
can	O
be	O
achieved	O
if	O
differences	O
are	O
subsequently	O
entropy	B-Algorithm
coded	I-Algorithm
because	O
the	O
entropy	O
of	O
the	O
difference	O
signal	O
is	O
much	O
smaller	O
than	O
that	O
of	O
the	O
original	O
discrete	O
signal	O
treated	O
as	O
independent	O
samples	O
.	O
</s>
<s>
DPCM	B-General_Concept
was	O
invented	O
by	O
C	O
.	O
Chapin	O
Cutler	O
at	O
Bell	O
Labs	O
in	O
1950	O
;	O
his	O
patent	O
includes	O
both	O
methods	O
.	O
</s>
<s>
The	O
encoder	O
performs	O
the	O
function	O
of	O
differentiation	O
;	O
a	O
quantizer	B-Algorithm
precedes	O
the	O
differencing	O
of	O
adjacent	O
quantized	O
samples	O
;	O
the	O
decoder	O
is	O
an	O
accumulator	O
,	O
which	O
if	O
correctly	O
initialized	O
exactly	O
recovers	O
the	O
quantized	B-Algorithm
signal	I-Algorithm
.	O
</s>
<s>
The	O
incorporation	O
of	O
the	O
decoder	O
inside	O
the	O
encoder	O
allows	O
quantization	B-Algorithm
of	O
the	O
differences	O
,	O
including	O
nonlinear	O
quantization	B-Algorithm
,	O
in	O
the	O
encoder	O
,	O
as	O
long	O
as	O
an	O
approximate	O
inverse	O
quantizer	B-Algorithm
is	O
used	O
appropriately	O
in	O
the	O
receiver	O
.	O
</s>
<s>
When	O
the	O
quantizer	B-Algorithm
is	O
uniform	O
,	O
the	O
decoder	O
regenerates	O
the	O
differences	O
implicitly	O
,	O
as	O
in	O
this	O
simple	O
diagram	O
that	O
Cutler	O
showed	O
:	O
</s>
