JPS62294390A - Transmission system for digital audio signal - Google Patents

Abstract

PURPOSE:To economically construct the transmission system of a digital audio signal, by constituting a system so that the digital audio signal reproduced by a compact disk player is transmitted to a CATV line being left as an EFM modulation signal. CONSTITUTION:The EFM modulation signal(signal before applying EFM demodulation) is derived from a compact disk player 1, and its high frequency component is cut at a low-pass filter 3. The output of the low-pass filter 3 is impressed on an amplitude modulation circuit 4, and an IF frequency signal(carrier signal) outputted from an oscillation circuit 5 is amplitude-modulated based on the EFM modulation signal. The modulation signal passes through a residual sideband filter(VSBF) 6, and is impressed on a mixing circuit 7, and is mixed with a local oscillation frequency signal corresponding to each output channel outputted from a local oscillation circuit 8, and after passing through a band-pass filter 9, it is mixed with another CATV signal at a combiner, then it is sent to the CATV line.

Description

[Detailed description of the invention]

3. Detailed explanation of the invention a. INDUSTRIAL APPLICATION FIELD The present invention is an OCX. [American technology When transmitting digital audio signal No. N, the digital audio signal has a high bit rate and therefore a wide transmission band. 10,000, CA'l"V line'iyF++ When transmitting with RC. Transmission line efficiency? It is preferable to take into account the transmission in as narrow a band as possible. Time division multiplexing and multi-level methods are being considered as methods for transmitting all of the many digital audio channels.

[For example, in the 1970s
9-15387]. C. Problems solved by the invention The sources of digital audio signals transmitted using CATV twin T-types can be easily and plentifully introduced using compact discs, which are now becoming popular. The source of the digital audio signal transmitted there is limited to FC18. When using a time-division multiplexing method f multi-level method such as the Somai technology, -f:
A proprietary (different from compact disc system) signal format for ? In addition, the circuits 1fg on the transmitting side and the receiving side are also complicated. Therefore. The present invention is limited to the source gold compact disc of Digital Audio No. 1n, without complicating the circuit configurations on the transmitting side and the receiving side. This invention proposes an economical system for transmitting digital audio signals.20 Means for Solving ProblemsIn the present invention, on the transmitting side, a compact disc player is used to generate a compact disc. LIJ play n
The Ef'M modulated digital audio signal as it is (
In other words, EFM has been reinstated, and digital processing MA such as error correction has been implemented.
The transmission rate of the EFM modulated digital audio signal in the Rojo 0 effect compact disk system is 4.321 BMbpa, which is configured to perform amplitude modulation and transmit it to the CATV line without performing any digital/analog conversion.
However, the 8 wave number components of this signal are maximum 72QKHz and minimum 196Kdz, and the cutoff F of the compact disc player's big amplifier.
Of course, if the wave number is 1.44M11z, the transmission band is 1.5M14Z or 2MHz.
It is sufficient. Therefore, it is possible to transmit digital audio signals of 572 channels (sources) per 1 channel (6 MHz) of television. (An 11-step EFM modulated signal (signal before EFM demodulation) is derived, and the high frequency component is removed by a low-pass filter (3). FIG. 4 shows the complete frequency % characteristic diagram of this filter (3). The output of the low-pass filter (3) is applied to the amplitude modulation circuit (4), and the oscillation circuit (5)
The IF' frequency signal (ΦYaria signal) output from the IF' frequency signal is amplitude-modulated based on the EFM modulation signal. This modulated signal passes through the vestigial sideband filter (VSBF (i7) and is not applied to the mixing circuit (7). The carrier frequency matches the IF' frequency.The mixing circuit (7) is fired and the local oscillation circuit (8) outputs the local oscillation frequency e signal corresponding to the valley output channel and the mixing 1 to the band pass filter (9). )'. It is mixed with other CATV (q) in a combiner (described later) and sent to CATV ray V. Note that three channels worth of audio signals are transmitted for one television channel. In this case, the IF frequency or the local oscillation frequency should be shifted to vi-5 steps. In CATv terminals (A), the channel of the selected frequency is the 1st television channel (91
, 25MHE) or Television Channel 2 (
97.25 MHz) fixed foot channel vC frequency converted. In the PCM Tartar CD, when the television channel is selected, the RF' switch (a
Output is derived from the J side terminal, and a signal is printed DH to the television receiver. When the audio channel is selected, an output is derived from the opposite terminal of the RF switch, and the PCM turn signal CυVC is applied. PC
Mter ζ naru! A signal processing circuit 241 for a conventionally known compact disc player, CATV, and PCM system can be constructed. CATV terminal (2
The signal manually inputted from 01 is band-limited by the band-pass filter that uses the fixed channel frequency J→band as described above to remove the influence of adjacent channel signals, and is then transferred to the amplifier circuit @Tai-I (AM detection circuit Cη Amplification 1
An automatic gain control circuit (to) is provided between the insect path (to) and the AM@wave circuit α power. EF'M signal demodulated by AM detection circuit (2) Transversal filter czcavc
One slicer group performs waveform equalization and is shaped into a rectangular wave (g).The existence of this waveform-shaped EFM signal is
When detected by the F'M signal detection circuit clIJ, the two-circuit switch (to) is switched to the b side (OATV[), and the signal processing circuit (from 241iillIl, that is, the slide
The EF'M signal from the mountain is applied to the digital signal processing circuit G·υ of the compact disc player Q via the switch. The digital signal processing circuit C34J has a conventionally well-known configuration, and includes an EFM signal demodulation circuit, an error detection/correction circuit, and the like. The clock for digital signal processing can be obtained from the voltage controlled oscillation circuit C4. That is,
In an externally synchronized PLL circuit, the edge v of the EFM signal
The clock (reference) created based on C and the output of the oscillation circuit are compared in phase with the signal frequency-divided by the divider included in the signal processing circuit diagram, and the oscillation circuit is activated using this phase comparison output.
kllll control one oscillation from VC lol! r- from E
A clock synchronized with an FM signal can be demodulated. This clock can be used as a clock for all-digital signal processing. The digital signal output from the digital signal processing (b) path (b) is converted into left and right audio signals by the D-AR conversion circuit. To explain a little about the configuration of the conventionally known compact disc player included in the PCM turnnal] J, the signal detected by the pickup c37) from the Elidisc 0 is waveform-rectified by the analog waveform shaping circuit (g), and this signal is (EF'M signal) is applied to the digital signal processing circuit diagram through the a-side contact of the switcharo, and F2FM demodulation, error detection/correction, etc. are performed as is conventionally known. Output between analog and waveform shaping circuits is also applied to the end of the system control circuit, and a 1-focus control cape signal and a tracking error signal are created. is 2%
be done. Furthermore. The servo circuit 0υ also controls the Eris spindle motor t43. FIG. 6 schematically shows a system that combines a conventional CATV system and a digital audio signal transmission system according to the present invention. On the transmitting side, the digital audio signal is sent to the compact disc player (as described above).
1) and residual W side band-AM narrow band modulator (2) [This includes G (amplitude modulation circuit Mf4), residual sideband filter (6), mixing circuit (7), etc. shown in Figure 1. configured] and applied to combiner 4. In the illustrated implementation, there are three sets of players (1) and transformers (2J
'Used to frequency multiplex and transmit three audio signal sources into one television channel. A plurality of types of television signals processed in the same manner as in a normal CATV system and various data signals such as an ID number for a CATV terminal are applied to the combiners a and O. This (0
7'-#M@ba system control computer U
The signal υ is modulated by the FSK modulator u4 and applied to the combiner α1. The signal transmitted by the CATV line is first applied to the CATV terminal (2). CATV Turnal (211
When a television signal is selected on 1&C, it is output to the television receiver (43 side) on 1gI.
The CM turn signal (2JJK is applied and demodulated into an analog audio signal) is outputted to the amplifier circuit 1441 and then to the speaker. The EFM modulated digital audio signal is transmitted to the CATV line as it is, so a conventional compact disc player can be used.
J: An easy and straightforward digital audio signal transmission system? It's a monkey if you build an ellipse.

[Brief explanation of drawings]

Figures 1 to 3 show the digital audio signal transmission system according to the present invention.
Block diagram of Au mounting d. FIG. 2 is a diagram showing a block diagram of the receiving side device;
FIG. 6 is a simplified T-bottom diagram of the entire system. FIG. 4 is a characteristic diagram of the low-pass filter, and FIG. 5 is a characteristic diagram of the shallow miwa 111ilA# filter.

Claims (1)

[Claims] (1) A digital audio signal transmission method using a cable television line, in which the EFM modulated digital audio signal played from a compact disc is amplitude-modulated using a compact disc player on the transmitting side, and the cable TV A digital audio signal transmission method characterized by transmitting to the receiving side using John line.