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Digital BTSC compander system
| Details |
Inventors: Easley, Matthew Frank;
Assignee: Antec Corporation (Duluth, GA)
Primary Examiner: Kostak; Victor R.
Assistant Examiner:
Attorney, Agent or Firm:
An apparatus for generating a broadcast television stereo signal has a left channel and a right channel. An analog-to-digital converter converts the right-channel signal to a right digital signal and the left-channel to a left digital signal. A circuit, which could include a digital signal processing chip, generates a first signal that includes the right digital signal added to the left digital signal and generates a second signal that includes the right digital signal subtracted from the left digital signal. The circuit also generates a digitally pre-emphasized first signal, which includes digital pre-emphasis, and a digitally pre-emphasized second signal, which also includes digital pre-emphasis. The circuit transforms the pre-emphasized first signal to a digital BTSC L+R signal and transforms the pre-emphasized second signal to a digital BTSC L-R signal. A digital-to-analog converter converts the digital BTSC L+R signal to an analog BTSC L+R signal and the digital BTSC L-R signal to an analog BTSC L-+R signal. The analog BTSC L+R and L-R signals are then modulated onto a carrier wave. |
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DETAILED DESCRIPTION OF THE INVENTION The BTSC Specification is intended to serve the industry in the form of recommendations for anyone wishing to practice multichannel television sound (MTS) in accordance with the BTSC system and the FCC Rules governing its use.
OST Bulletin No.
60 gives a technical description of the BTSC system.
The BTSC Specification and OST Bulletin No.
60 are jointly referred herein as the BTSC Standard.
The BTSC Standard is intended for equipment manufacturers and broadcasters, providing the manufacturers with information useful in making design tradeoffs and recommended performance standards.
For broadcasters, the BTSC Standard provides information to allow individual equipment items to be defined in terms of performance so that the transmitter plant will perform properly as a system.
Furthermore, the BTSC Standard identifies receiver issues, which are of significance to the broadcaster and the receiver manufacturer.
The transmission standards are graphically illustrated in FIG.
1 and summarized in Table 1.
The main channel (L+R) signal 110, consists of the sum of left plus right audio signals.
The stereophonic subchannel (L-R) 112, consists of a double-sideband AM modulated carrier.
FIG.
2 is a functional block diagram of the BTSC compatible television transmitter 200, and FIG.
3 is functional block diagram of a corresponding BTSC compatible television receiver 300.
The transmitter of FIG.
2 and the receiver of FIG.
3 could be employed in both existing devices and the present invention.
Referring to FIG.
1 and Table 1, the main-channel aural-carrier modulation consists of an (L+R) audio signal subjected to 75 .
mu.
s preemphasis.
The (L-R) audio signal is subjected to compression, that is, the transmitter part of the companding system that includes complementary expansion in the receiver.
The compressed (L-R) signal causes double-sideband, suppressed-carrier amplitude modulation of a subcarrier at 2 f.
sub.
H where f.
sub.
H is the transmitted picture horizontal scanning frequency, 15
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Audio Signal Processing 
