T H A T
C o r p o r a t i o n
dbx-
TV Noise Reduction
Systems
THAT
525CH, 525EH
FEATURES
Unique Spectral Companding
System
Strong Noise Reduction (up to
50 dB)
Flat Frequency Response: Typ
+/-0.6 dB (Back-to-Back)
Low Distortion: Typ 0.1%
Excellent Subjective Quality,
Even With Very Noisy Channels
35 dB Midband Separation in
BTSC-TV Applications
APPLICATIONS
Broadcast TV Modulators
Cable TV Modulators
BTSC Monitor Receivers
Satellite Communications
Terrestrial Microwave Links
Cable Transmission Links
Fiber Optic Links
Digital Encoders (A/D/A)
DESCRIPTION
The THAT 525CH and 525EH cards are broad-
cast-quality circuit boards originally developed to
conveniently implement the dbx-TV noise-reduction
portion of the BTSC Multichannel Television Sound
system. In a properly designed modulator, the
cards offer performance exceeding FCC require-
ments for separation, dynamic range, frequency re-
sponse and distortion of BTSC signals. Based on a
highly effective combination of wideband and spec-
tral companding algorithms, the system is also ap-
plicable to any analog or digital audio channel with
an uncompanded signal-to-noise ratio as low as
26dB.
Basic Operation
The dbx-TV system operates by compressing the
dynamic range of the program audio before trans-
mission, and then expanding the dynamic range
upon reception. In the compression cycle, a 2:1
(wideband) compression ratio is applied across the
entire audio spectrum while a spectral compressor
simultaneously varies the signal preemphasis
based on the high frequency content of the pro-
gram material. The spectrum of the resulting com-
pressed signal resembles white noise, which
provides optimal masking of channel noise in FM
transmission systems.
In the expansion cycle, the processing is in-
verted. The signal is expanded by a (wideband)
ratio of 1:2, while the spectral expander varies the
deemphasis to complement the compressor's dy-
namic preemphasis characteristic. When program
signal is absent or low in level, channel noise is
thus drastically reduced. During higher level pas-
sages the 525 cards use the signal itself to effec-
tively mask channel noise
The result is a system which delivers CD-like
audio quality with a channel dynamic range as low
as 40 dB.
Compressors and Expanders
The 525CH is the compressor, used to encode
signals before transmission. It is typically used in
broadcast television and CATV transmitters to en-
sure the highest quality encoding possible. The
525EH is the complementary expander for decod-
ing signals after reception. It is typically used in
monitor receivers.
Other applications of the 525 Series noise reduc-
tion cards include reduced bit-rate digital encoders
and low-dynamic range analog transmission sys-
tems.
dbx
is a registered trademark of Carillon Electronics Corporation
THAT Corporation; 734 Forest Street; Marlborough, Massachusetts 01752; USA
Tel: (508) 229-2500; Fax: (508) 229-2590 Web: http://www.thatcorp.com
SPECIFICATIONS
1
Absolute-Maximum Ratings (T
A
= 25C)
Positive Supply Voltage (V
CC
)
+18 V
Negative Supply Voltage (V
EE
)
18 V
Supply Current (I
CC
)
100 mA
Power Dissipation (P
D
)
3.6 W
Operating Temperature Range (TOP)
10 to 40C
Storage Temperature Range (TST)
20 to +75C
Recommended Operating Conditions
525CH
525EH
Parameter
Symbol
Conditions
Min
Typ
Max
Min
Typ
Max
Units
Positive Supply Voltage
V
CC
11.95 12.00 12.05
11.95 12.00 12.05
V
Negative Supply Voltage
V
EE
11.95 12.00 12.05
11.95 12.00 12.05
V
Electrical Characteristics
2
525CH
525EH
Parameter
Symbol
Conditions
Min
Typ
Max
Min
Typ
Max
Units
Supply Current
I
CC
No Signal
--
56
100
--
56
100
mA
Input Impedance
R
IN
19.8
20.0
20.2
19.8
20.0
20.2
k
Output Impedance
R
OUT
1
1
Input Level
300 Hz, 100% EIM
3
3.535 3.540 3.544
1.328 1.330 1.332
Vrms
Output Level
300 Hz, 100% EIM
3
1.328 1.330 1.332
3.535 3.540 3.544
Vrms
Swept Sine Wave Response
4
20 ~ 100 Hz
-0.15
0
+0.15
-0.3
0
+0.3
dB
100 ~ 8,000 Hz
-0.07
0
+0.07
-0.2
0
+0.2
dB
8,000 ~ 14,000 Hz
-0.2
0
+0.2
-0.6
0
+0.6
dB
Total Harmonic Distortion
THD
300 mV, 15 kHz Bandwidth
Measured through encode/decode cycle --
0.1
0.2
--
0.1
0.2
%
Equivalent Input Noise
e
n in
15 kHz Bandwidth
--
200
--
--
--
200
V
0dB-Gain Input Level Unaffected Level
300 Hz
--
500
--
--
500
--
mV
Dimensions
L x W
4 x 5.5
4 x 5.5
inches
Component Height
Above Board
--
--
0.7
--
--
0.7
inches
Below Board
--
--
0.25
--
--
0.25
inches
Connectors (optional)
4-pin & 6-pin Molex
4-pin & 6-pin Molex
1. All specifications subject to change without notice.
2. Unless otherwise noted, T
A
=25C, V
CC
= +12V, V
EE
= -12V.
3. 100% EIM (Equivalent Input Modulation) is that level which would cause 100% modulation of the LR subcarrier if
the 525CH were replaced with a 75-
sec preemphasis network. See the EIA's BTSC Recommended Practices for
more details.
4. Response is given in deviation from the theoretical ideal curves for
dbx
-TV (BTSC) compression/expansion.
Rev 10/27/96
THAT Corporation; 734 Forest Street; Marlborough, Massachusetts 01752; USA
Tel: (508) 229-2500; Fax: (508) 229-2590 Web: http://www.thatcorp.com
PDF 
ZIP