<s>
A	O
delta	B-General_Concept
modulation	I-General_Concept
(	O
DM	O
or	O
Δ-modulation	O
)	O
is	O
an	O
analog-to-digital	O
and	O
digital-to-analog	O
signal	O
conversion	O
technique	O
used	O
for	O
transmission	O
of	O
voice	O
information	O
where	O
quality	O
is	O
not	O
of	O
primary	O
importance	O
.	O
</s>
<s>
DM	O
is	O
the	O
simplest	O
form	O
of	O
differential	B-General_Concept
pulse-code	I-General_Concept
modulation	I-General_Concept
(	O
DPCM	B-General_Concept
)	O
where	O
the	O
difference	O
between	O
successive	O
samples	O
is	O
encoded	O
into	O
n-bit	O
data	O
streams	O
.	O
</s>
<s>
In	O
delta	B-General_Concept
modulation	I-General_Concept
,	O
the	O
transmitted	O
data	O
are	O
reduced	O
to	O
a	O
1-bit	O
data	O
stream	O
.	O
</s>
<s>
Only	O
the	O
change	O
of	O
information	O
is	O
sent	O
,	O
that	O
is	O
,	O
only	O
an	O
increase	O
or	O
decrease	O
of	O
the	O
signal	O
amplitude	O
from	O
the	O
previous	O
sample	O
is	O
sent	O
whereas	O
a	O
no-change	O
condition	O
causes	O
the	O
modulated	B-Application
signal	O
to	O
remain	O
at	O
the	O
same	O
0	O
or	O
1	O
state	O
of	O
the	O
previous	O
sample	O
.	O
</s>
<s>
To	O
achieve	O
high	O
signal-to-noise	O
ratio	O
,	O
delta	B-General_Concept
modulation	I-General_Concept
must	O
use	O
oversampling	O
techniques	O
,	O
that	O
is	O
,	O
the	O
analog	O
signal	O
is	O
sampled	O
at	O
a	O
rate	O
several	O
times	O
higher	O
than	O
the	O
Nyquist	O
rate	O
.	O
</s>
<s>
Derived	O
forms	O
of	O
delta	B-General_Concept
modulation	I-General_Concept
are	O
continuously	B-Algorithm
variable	I-Algorithm
slope	I-Algorithm
delta	I-Algorithm
modulation	I-Algorithm
,	O
delta-sigma	O
modulation	B-Application
,	O
and	O
differential	O
modulation	B-Application
.	O
</s>
<s>
Differential	B-General_Concept
pulse-code	I-General_Concept
modulation	I-General_Concept
is	O
the	O
superset	O
of	O
DM	O
.	O
</s>
<s>
Rather	O
than	O
quantizing	O
the	O
value	O
of	O
the	O
input	O
analog	O
waveform	O
,	O
delta	B-General_Concept
modulation	I-General_Concept
quantizes	O
the	O
difference	O
between	O
the	O
current	O
and	O
the	O
previous	O
step	O
,	O
as	O
shown	O
in	O
the	O
block	O
diagram	O
in	O
Fig.1	O
.	O
</s>
<s>
The	O
modulator	B-Application
is	O
made	O
by	O
a	O
quantizer	O
which	O
converts	O
the	O
difference	O
between	O
the	O
input	O
signal	O
and	O
the	O
integral	O
of	O
the	O
previous	O
steps	O
.	O
</s>
<s>
The	O
integrator	O
itself	O
constitutes	O
a	O
low-pass	B-Algorithm
filter	I-Algorithm
.	O
</s>
<s>
The	O
two	O
sources	O
of	O
noise	O
in	O
delta	B-General_Concept
modulation	I-General_Concept
are	O
"	O
slope	O
overload	O
"	O
,	O
when	O
step	O
size	O
is	O
too	O
small	O
to	O
track	O
the	O
original	O
waveform	O
,	O
and	O
"	O
granularity	O
"	O
,	O
when	O
step	O
size	O
is	O
too	O
large	O
.	O
</s>
<s>
In	O
delta	B-General_Concept
modulation	I-General_Concept
there	O
is	O
a	O
restriction	O
on	O
the	O
amplitude	O
of	O
the	O
input	O
signal	O
,	O
because	O
if	O
the	O
transmitted	O
signal	O
has	O
a	O
large	O
derivative	O
(	O
abrupt	O
changes	O
)	O
then	O
the	O
modulated	B-Application
signal	O
can	O
not	O
follow	O
the	O
input	O
signal	O
and	O
slope	O
overload	O
occurs	O
.	O
</s>
<s>
If	O
the	O
communication	O
channel	O
is	O
of	O
limited	O
bandwidth	O
,	O
there	O
is	O
the	O
possibility	O
of	O
interference	O
in	O
either	O
DM	O
or	O
PCM	B-Algorithm
.	O
</s>
<s>
Hence	O
,	O
'	O
DM	O
 '	O
and	O
'	O
PCM	B-Algorithm
 '	O
operate	O
at	O
same	O
bit-rate	O
which	O
is	O
equal	O
to	O
N	O
times	O
the	O
sampling	O
frequency	O
.	O
</s>
<s>
Adaptive	O
delta	B-General_Concept
modulation	I-General_Concept
(	O
ADM	O
)	O
was	O
first	O
published	O
by	O
Dr.	O
John	O
E	O
.	O
Abate	O
(	O
AT&T	O
Bell	O
Laboratories	O
Fellow	O
)	O
in	O
his	O
doctoral	O
thesis	O
at	O
NJ	O
Institute	O
Of	O
Technology	O
in	O
1968	O
.	O
</s>
<s>
In	O
the	O
mid-1980s	O
,	O
Massachusetts	O
audio	O
company	O
DBX	O
marketed	O
a	O
commercially	O
unsuccessful	O
digital	O
recording	O
system	O
based	O
on	O
adaptive	O
delta	B-General_Concept
modulation	I-General_Concept
.	O
</s>
<s>
Adaptive	O
delta	B-General_Concept
modulation	I-General_Concept
or	O
Continuously	B-Algorithm
variable	I-Algorithm
slope	I-Algorithm
delta	I-Algorithm
modulation	I-Algorithm
(	O
CVSD	B-Algorithm
)	O
is	O
a	O
modification	O
of	O
DM	O
in	O
which	O
the	O
step	O
size	O
is	O
not	O
fixed	O
.	O
</s>
<s>
This	O
error	O
can	O
be	O
reduced	O
by	O
using	O
a	O
low-pass	B-Algorithm
filter	I-Algorithm
.	O
</s>
<s>
ADM	O
provides	O
robust	O
performance	O
in	O
the	O
presence	O
of	O
bit	O
errors	O
meaning	O
error	O
detection	O
and	O
correction	O
are	O
not	O
typically	O
used	O
in	O
an	O
ADM	O
radio	O
design	O
,	O
it	O
is	O
this	O
very	O
useful	O
technique	O
that	O
allows	O
for	O
adaptive-delta-modulation	O
.	O
</s>
<s>
Contemporary	O
applications	O
of	O
Delta	B-General_Concept
Modulation	I-General_Concept
includes	O
,	O
but	O
is	O
not	O
limited	O
to	O
,	O
recreating	O
legacy	O
synthesizer	O
waveforms	O
.	O
</s>
<s>
For	O
example	O
,	O
the	O
C64DTV	B-Device
used	O
a	O
32MHz	O
sample	O
rate	O
,	O
providing	O
ample	O
dynamic	O
range	O
to	O
recreate	O
the	O
SID	O
output	O
to	O
acceptable	O
levels	O
.	O
</s>
<s>
Delta	B-General_Concept
Modulation	I-General_Concept
was	O
used	O
by	O
Satellite	O
Business	O
Systems	O
or	O
SBS	O
for	O
its	O
voice	O
ports	O
to	O
provide	O
long	O
distance	O
phone	O
service	O
to	O
large	O
domestic	O
corporations	O
with	O
a	O
significant	O
inter-corporation	O
communications	O
need	O
(	O
such	O
as	O
IBM	O
)	O
.	O
</s>
<s>
The	O
voice	O
ports	O
used	O
digitally	O
implemented	O
24	O
kbit/s	O
delta	B-General_Concept
modulation	I-General_Concept
with	O
Voice	O
Activity	O
Compression	O
(	O
VAC	O
)	O
and	O
echo	O
suppressors	O
to	O
control	O
the	O
half	O
second	O
echo	O
path	O
through	O
the	O
satellite	O
.	O
</s>
<s>
They	O
performed	O
formal	O
listening	O
tests	O
to	O
verify	O
the	O
24	O
kbit/s	O
delta	O
modulator	B-Application
achieved	O
full	O
voice	O
quality	O
with	O
no	O
discernible	O
degradation	O
as	O
compared	O
to	O
a	O
high	O
quality	O
phone	O
line	O
or	O
the	O
standard	O
64kbit/s	O
μ-law	B-Algorithm
companded	B-Algorithm
PCM	B-Algorithm
.	O
</s>
<s>
The	O
original	O
proposal	O
in	O
1974	O
,	O
used	O
a	O
state-of-the-art	O
24kbit/s	O
delta	O
modulator	B-Application
with	O
a	O
single	O
integrator	O
and	O
a	O
Shindler	O
Compander	B-Algorithm
modified	O
for	O
gain	O
error	O
recovery	O
.	O
</s>
<s>
The	O
final	O
implementation	O
replaced	O
the	O
integrator	O
with	O
a	O
Predictor	O
implemented	O
with	O
a	O
two	O
pole	O
complex	O
pair	O
low-pass	B-Algorithm
filter	I-Algorithm
designed	O
to	O
approximate	O
the	O
long	O
term	O
average	O
speech	O
spectrum	O
.	O
</s>
<s>
A	O
nearly	O
perfect	O
Shindler	O
Compander	B-Algorithm
replaced	O
the	O
modified	O
version	O
.	O
</s>
<s>
It	O
was	O
found	O
the	O
modified	O
compander	B-Algorithm
resulted	O
in	O
a	O
less	O
than	O
perfect	O
step	O
size	O
at	O
most	O
signal	O
levels	O
and	O
the	O
fast	O
gain	O
error	O
recovery	O
increased	O
the	O
noise	O
as	O
determined	O
by	O
actual	O
listening	O
tests	O
as	O
compared	O
to	O
simple	O
signal	O
to	O
noise	O
measurements	O
.	O
</s>
<s>
The	O
final	O
compander	B-Algorithm
achieved	O
a	O
very	O
mild	O
gain	O
error	O
recovery	O
due	O
to	O
the	O
natural	O
truncation	O
rounding	O
error	O
caused	O
by	O
twelve	O
bit	O
arithmetic	O
.	O
</s>
<s>
The	O
complete	O
function	O
of	O
delta	B-General_Concept
modulation	I-General_Concept
,	O
VAC	O
and	O
Echo	O
Control	O
for	O
six	O
ports	O
was	O
implemented	O
in	O
a	O
single	O
digital	O
integrated	O
circuit	O
chip	O
with	O
twelve	O
bit	O
arithmetic	O
.	O
</s>
<s>
A	O
single	O
digital-to-analog	O
converter	O
(	O
DAC	O
)	O
was	O
shared	O
by	O
all	O
six	O
ports	O
providing	O
voltage	O
compare	O
functions	O
for	O
the	O
modulators	B-Application
and	O
feeding	O
sample	O
and	O
hold	O
circuits	O
for	O
the	O
demodulator	O
outputs	O
.	O
</s>
