The owners of a number of imported TV sets do not have the opportunity to use such the function of the machines of foreign production, stereo sound support of broadcast and cable television programs. Often only those who makes the satellite program, I can appreciate its advantage. How - the transmission of television sound in the existing standards and how to improve his play told in a published article.
Technical base of national television in recent years, much improved. On the television there is a new technique that uses modern tools and technologies for the preparation and conduct of gear. Improved the quality image, a growing number of broadcasting channels. The only feature not undergone significant changes in broadcast and cable television, in - sound. For decades it remained monaural.
Monaural sound seems to be coming from a single point, the speaker. In television, as in the movie, this way of playing is in conflict with the image. He partly acceptable only when showing close UPS, when the sound must proceed from the center of the screen. In case of medium and the logically required the expansion of the sound image in front of the audience.
Dramatically improve the perception of the soundscape can provide only multichannel system of the formation and reproduction of sound. This is numerous variants of the two-channel stereo, four-channel Quad, five - channel surround sound systems. All of them (except Quad, has not yet found wide application) brought to high circuit quality level that is industrially developed and used all over the world. Recently they appeared in our country. Consider their basic parameters.
The VHS format VCRs simple design played a sound one channel, and more complex (Hi-Fi) - and even on two. The mode in which recorded the sound is usually marked on the videotape. It may be STEREO, DOLBY STEREO, DOLBY SURROUND (multi-channel sound). The absence of such label means mono recording. On the media used VHS format S-VHS and CD players mini DVDs record is done almost always with multi-channel sound. All these devices are treated audio signals, typically at a low frequency in analog form, and players DVD and digital.
Telecentres foreign countries convey the sound is different ways.
In the U.S. system is used BTSC MTS (Broadcast Television Systems Committee - Multichannel Television Sound - multi-channel television sound - standard Committee for television transmitting systems). She represents the monaural TV standard NTSC-M, which allowed further to introduce a multi-channel sound. The system includes subcarrier modulation frequency of 4.5 MHz is not a mono output and integrated stereo (KCC). Structure this signal is shown in Fig. 1,and. The frequency of the suppressed subcarrier signal L-R is $ 31,468 kHz, which corresponds to the second harmonic of the lower frequency equal to NTSC 15,734 kHz. In addition to the usual L+R, L-R, subjected to amplitude (AM) and balanced (BM) modulation, and the pilot signals, KCC BTSC MTS entered two more additional frequency-modulated coded audio channel on subcarrier 78,67 and 102,27 kHz (for official use). Receivers with monosialosyl tract perceive only the signal L+R. the Apparatus in which is provided stereotrack, process all the signals.
In Japan, the audio signals are also transmitted as CMP (Fig. 1,b), but is built otherwise than in BTSC MTS. Subcarrier signal L-R is not suppressed. The pilot tone too passed, but used only for recognizing the operation mode. When transferring stereogram he modulated tone frequency 982,5 Hz, dual channel (bilingual) the transfer of tone frequency 922,5 Hz, and in the case of mono the pilot signal is not modulated.
In standard PAL-B/G terrestrial broadcast signals are on PCTV subcarriers 5.5 and 5,742 MHz with FM modulation (Fig. 1). One of them passed the signal L+R, on the other - 2R. The use of the signal 2R is L-R allows to smooth the noise in the channels in the channel L is twice higher than in the channel R. This system is called Zweiton. In addition, the stereo signal is repeated in PCT digitally encoded system NICAM (Near Instantaneous Companded Audio Multiplex - a direct transmission dual sound) using AFM (relative phase manipulation).
PCTV PAL-I (Fig. 1,g) contains two simultaneously transmitted audio signal maintenance: frequency modulated analog mono signal on subcarrier 5,9996 MHz and a digital stereo signal on subcarrier 6,552 MHz, encoded by system NICAM.
Stereo system NICAM is formed on the telecentre by discretizing analog signals L and R in time with a sampling rate of 32 kHz and quantization 256 levels (8 bits) in each sample. Information from both channels is passed in the General flow DQPSK digital data (Digital Quadrature Phase Shift Keying - the flow of digital data with a quadrature phase shift) at a rate of 728 kbit/s. This stream modulating the subcarrier audio (5,85 MHz PAL-B/G and 6,552 MHz in РАL-I) method OFM.
In the TV thread DQPSK is decoded and converted into two-channel analog the signals L and R. the structure of the decoder is presented in Fig. 2.
In DD1 chip from the demodulator PCTV comes sound subcarrier modulated stream DQPSK and the pilot signal with a frequency 54,6875 kHz. In DD1 chip subcarriers demodulated and received digital stream is cleared from interference in the digital filter. Stream DQPSK and the pilot tone is transmitted to the decoder DD2. Decoding is to divide the flow DQPSK for digital signals L and R, and also to break it up into groups of bits (words) corresponding to the samples Digital-to-analog converters in the chip DD2 transform of the digital samples in pulses which after smoothing analog form the signals L and R. At the same time is recognized and the method of sound transmission. If the pilot tone modulated frequency 117,5 Hz, is transmitted to stereogram, if the frequency of 274.1 Hz - two mono, but if not modulated - one mono. The decoder is controlled microcontroller control system to the TV via digital I2C bus.
All considered compatible with the Park monaural TVs.
Television broadcasting in the satellite channels are organized with the transmission of signals in analog, digital-to-analogue and digital forms.
In an analogue form continues satellite broadcasting in NTSC, PAL, SECAM. In the system SECAM-D/K sound, as before, remains mono. On satellite channels, in contrast to terrestrial broadcasting, it is transmitted on subcarriers 6,8; 7 or 7.5 MHz.
In the PAL system the sound is in analog form, are arranged one by one two or four channels. In the first case, choose one of subcarriers 6,5; 6,6; 6,65; 6,8; 7; 7.5 MHz. Two - and four-channel audio is provided by system Wegener-Panda 1. As shown in Fig. 1,d, it provides the inclusion in PCTV four additional frequency-modulated sound subcarriers 7,02; 7,2; 7,38; 7,56 MHz. Two of them are used to transfer stereo accompaniment of the television program, the rest for simultaneously transmitted radio programs. Learn more about this the system can be found in [1].
Digital sound analog PAL TV signal through satellite passed after encoding system NICAM.
In digital to analogue form of the television signals used in the MAC systems and MUSE.
The MAC (Multiple Analog Components - seal analog component) represents a transition from analogue to digital transmission methods TV signals via the communication channels. It applied to separate analog and in time the transmission of the luminance signal and chrominance digital signal transmission sound and other information (the synchronization signals, Teletext, service signals). The processing at the transmitting and receiving side is provided digital methods.
There are several options for building the system: A-MAC, B-MAC, C-MAC, D-MAC, D2-MAC, HD-MAC, HD-B-WT. Their main differences lie in the ways signal coding, carrier modulation, the number of audio channels.
The sound signals from analog form is converted to digital after sampling them with a frequency of 32 kHz and quantization using 14 bits per sample. After they in real time written in the buffer memory, where connect to the digital information into packets of 751 bits. Within the frame 162 is formed of a package in systems C-MAC, D-MAC (82 package D2-MAC). In the blanking intervals of the packets read Xia from the buffer memory at a speed of In 20.25 MHz portions 195 of bits in the string (10,125 MHz and 99 bits in the system D2-MAC) and in digital form are introduced into the transmitted television signal.
In the systems A-WT and C-WT digital signals placed on its podne-things 7,25 MHz, the system AND the MAC transmit them continuously.
Digital package represent a stream of bits that control the phase carrier of a television signal, which can take two or four fixed values.
System A-WT - single-channel. in variants B-D can be arranged for up to eight channels sound.
At the receiver, the digital sound signals are separated from the digital information, recorded into the buffer memory from which to read the digital-to-analog conversion at normal speed.
The MAC system has withstood the test of time. In the summer of 1999, more than 5000 satellite TV worked only 56 in standard D2-MAC and 20 in the standard IN-WT.
Options HD-MAC and HD-B-MAC refers to television systems, high definition (HDTV or HDTV) with scan at 1250 lines. They saved used in previous versions of the principles of digital sound and separated in time by analog signals for brightness and color. Learn more about the MAC system written in[2 and 3].
System MUSE (Multiple Sub-Nyquist tests Sampling Encoding system encoding multiple downsample to Nyquist) developed and used only in one television channel in Japan. In it, as in the MAC system, transmitted analog signals for brightness and color with digital signals and digital sound information. Like HD-MAC it is a system of high-definition (1125 lines)
The audio signal in the MUSE system together with digital information is transmitted in the blanking intervals field image using a four-phase carrier modulation at the transmission rate of 2,048 Mbit/s. More details the system is contained in [3].
There are also widely used digital compression system television information MPEG (Moving Picture Experts Group - development made by the group experts at moving images: MPEG-1, MPEG-2, MPEG-4. Their description is given in [2 and 4].
In broadcasting data compression takes place according to the system standards MPEG-2, which is used when drilling down to 625 lines. It consists of standards 20 levels of difficulty, allowing you to create algorithms for data compression in systems for various purposes. The audio portion of the standard system information compression audio channels MUSICAM (MPEG-Audio), allowing to handle up to six wideband audio high quality.
MPEG is the standard for digital television the lower level. Apart from these there are a set of harmonised standards for the transmission several television programs in the same frequency satellite (DVB-S), cable (DVB-C) or terrestrial (DVB-T) channels.
To resolve the contradictions between image and mono sound in a stationary TVs sometimes use a system of "mono surround", consisting of two speakers located on the sides of the screen. In TVs high class you can also add external speakers (AU).
In the equipment of foreign manufacture for this purpose, as a rule, the same type of compact broadband emitters of sound. In TV, produced in the former USSR, on the right side of the body is usually installed broadband head with a capacity of 3...4 W, while the left high-frequency, less power. Both the loudspeaker connected in parallel to the output of the common amplifier 3H. The sound is spatially extended. At the same time partially achieved pseudo stereophonic effect of frequency separation in space before the audience that improved the perception of the sound image. But placing several acoustic emitters in the General case open the TV could not to create a significant expansion of the sound volume.
To improve playback of monaural programs using methods of monoamine when a sound signal emitter is served without additional processing, on the other - after some delay. This allows to improve the acoustic properties of a room, giving him the desired hollowness. Like this method has not found wide application in monaural television and was popular only recently in intensive systems with multichannel sound.
You can use another method - with spatial pseudotropheus the division of the frequency spectrum of the sound, giving the bass on the right speaker, and high - to the left.
As for two-channel stereo playback systems sound, there are two basic methods of their construction: simple and extended stereo. In the first case, the sound signals received through the channels L and R. after amplification transmitted to the speakers without additional processing. The disadvantage of such systems is well known narrow spatial sound panorama unfolds not around listener, and before him in the form of a flat sound wall. The attempt to expand it, spreading out the speaker leads to the appearance in the center of the sound "picture" is clearly perceived failure.
Extended stereo increases the size of the stereo due to the transfer of part of the signal L to R channel, and Vice versa. If the transmitted signals are subjected to phase and temporal processing (delay), a landscape of sound can be significantly extended and in the case where the acoustic generators are located in a common housing on a small distance from each other.
There are two main variants of this system: ISS (Incredible Surround Sound - incredibly big sound) and system Qsound. In both cases, the audio signals processed chips - sound processors (RFP), which provide adjust the volume, balance, treble and bass. They also handled audio signals in mono modes, pseudostereo, simple and enhanced stereo stereo. There are a number of chips that implement these functions. This is TDA8421/24/25/26, TDA9860/61,
CXA1735AS, LMC1982CIN/CIV with I2C digital bus. They can include the processor TDA3810 performing only performance signal processing without their regulation.
SN is quite commonly used in TVs of different firms. So, chip TDA8425 TV TVT-C24F4R and forms it to pseudostereo when receiving broadcast signals system SECAM-D/K [5]. She applied at the receiver PHILIPS-FL [6]. Processor CXA1735AS works in a digital PANASONIC TV- TX-28WG25C (ODD) [7]. SONY TV-KV-28WS4R chip contains MSP3410, which combined the functions SN and decoder system NICAM [7].
Interesting solution low frequency audio path used in the TV PHILIPS - FL it has a Converter two-channel audio signal in five-channel with psevdoparabolicheskim the transformation algorithm. It structural diagram depicted in Fig. 3.
From a source of analog signals or from decoder NICAM stereo signals L and R come in ZP DA1, from him directly on amplifiers 3H A1 and A3, and then on the connected AC Parallel to L and R. they come to the adders S1 and S2, which are formed by the signals L+R and L-R. The first of them through a low pass filter through an amplifier A2 goes on Central AC M. the Signal L-R after the amplifier A4 is fed to the rear left and right AC SL and SR, connected in series with the counter United windings. This ensures that the antiphase signals on the speaker.
System advanced stereo and pseudocatatonia has improved the quality sound reproduction, but are unable to solve the problem of obtaining high-quality sound. Today it is formulated as: sound field must be large, to envelop the listener from all sides and from above,
ensuring the coincidence of the directions of the apparent sound sources with their the actual position in space when passing.
The problem of reproduction of such a sound was initially solved in the film, when appeared multi-channel surround-sound system in the concert halls - Dolby
Surround, THX and CS. Received at the same time, the wide distribution equipment home recording on a magnetic tape in the VHS format has led to a massive translation of movies on videocassettes for home viewing. In this case, naturally, there is a need to preserve the surround sound when overwriting the movie on videotape. This led to the creation of Dolby videonaruto Surround four-channel Dolby Pro Logic Surround with analogue performance of the audio signals and six-channel Dolby Digital with a digital representation.
In Dolby Pro Logic Surround provides for the conversion of multi-channel audio information in two-channel when recording to tape and return its transformation into a multichannel world? Sound information and coagulates deployed according to the algorithm, more complex than that used in pseudocatatonia. From the available sources the most complete description of the principles this system can be found in [8].
The conversion at the receiving side occurs in the audio decoder (DZ). Example the use of Dolby Pro Logic Surround may be the SONY TV- KV-28WS4R [7]. where DZ is the chip TC9337F-015. There are other such chips. for example. NJW1102AF. Speaker system model KV-28WS4R built the same as considered by the circuit of Fig. 3.
To emphasize the stereo effect and the best localization of sound CLE corrects the coefficient of transmission amplifiers for all channels so that he remained in the channel with the maximum signal level and has been reduced in the rest of us.
There are other options for building acoustic of the machine with volumetric sound. In the center above the TV sometimes impose additional broadband speakers to play sound from a source moving along the vertical. Rear speakers can not be located behind the viewer, and at the side of the one line with him. Instead of mono on them can be made pseudo stereophonic signals.
The logical conclusion of the process of improving systems of sound reproduction in television was the creation of the concept of home videoteacher. The composition and its opportunities are described in detail in [8 - 10]. His video production for TV or video projector with large screen TV, VCR, high class equipment to receive satellite programs. The audio - multi-channel amplifier multimode, PZ and DZ, the set AC.
So what can hams for improved playback TV sound?
First, I recommend to utilize the opportunity of watching movies with stereo sound. However, this would require a music center or any stereo system, VCR with stereotracks and videotapes index STEREO, DOLBY STEREO. Useful and practical advice you will find in [11].
If you go down that path, and get surround sound recorded on VHS index in DOLBY SURROUND version of DOLBY Pro Logic. But it will lead to serious trouble audio: 'll need DZ, four-channel amplifier and five remote AC.
Secondly, we can restrict the pseudo stereophonic sound reproduction support of broadcast and cable programs. But you have to modify the audio section of the TV, typing in the RFP, the second amplifier and AC 3H. More for detailed information about ZP are given in [12].
Literature
Author: B. Brylov, Moscow