Sound-in-Syncs is a method of multiplexing sound and video signals into a channel designed to carry video, in which data representing the sound is inserted into the line synchronising pulse of an

analogue television Analog television is the original television technology that uses analog signals to transmit video and audio. In an analog television broadcast, the brightness, colors and sound are represented by amplitude, phase and frequency of an analog ...

waveform. This is used on point-to-point links within broadcasting networks, including

studio/transmitter link A studio transmitter link (STL) sends a radio station's or television station's audio and video from the broadcast studio or origination facility to a radio transmitter, television transmitter or uplink facility in another location. This is accom ...

s (STL). It is not used for broadcasts to the public.

History

The technique was first developed by the BBC in the late 1960s. In 1966, The corporation's Research Department made a feasibility study of the use of

pulse-code modulation Pulse-code modulation (PCM) is a method used to digitally represent analog signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. In a PCM stream, the amplitud ...

(PCM) for transmitting television sound during the synchronising period of the video signal. This had several advantages: it removed the necessity for a separate sound link, reduced the possibility of operational errors and offered improved sound quality and reliability.Pawley, E (1972). ''BBC Engineering 1922-1972'', pp. 506-7, 522. BBC. .

Awards

Sound-in-Syncs and its R&D engineers have won several awards, including: * The

Royal Television Society The Royal Television Society (RTS) is a British-based educational charity for the discussion, and analysis of television in all its forms, past, present, and future. It is the oldest television society in the world. It currently has fourteen r ...

's Geoffrey Parr Award in 1972 * A

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in 1974 * In 1999, a

Technology & Engineering Emmy Award The Technology and Engineering Emmy Awards, or Technology and Engineering Emmys, are one of two sets of Emmy Awards that are presented for outstanding achievement in engineering development in the television industry. The Technology and Engineer ...

Versions

Original mono S-i-S

In the original system, as applied to 625 line analogue TV, the

audio signal An audio signal is a representation of sound, typically using either a changing level of electrical voltage for analog signals or a series of binary numbers for Digital signal (signal processing), digital signals. Audio signals have frequencies i ...

was sampled twice during each television line and each sample converted to 10-bit PCM. Two such samples were inserted into the next line synchronising pulse. At the destination, the audio samples were converted back to analogue form and the video waveform restored to normal. Compandors operating on the signal before encoding and after decoding enabled the required

signal-to-noise ratio Signal-to-noise ratio (SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. SNR is defined as the ratio of signal power to noise power, often expressed in deci ...

to be achieved. As the PCM noise was predominantly high-pitched, the compandor only needed to operate on the high frequencies. Also, the compandor only operated at high audio levels, so that modulation of the noise by the companding would be masked by the relatively loud high-frequency audio components. A pilot tone at half the sampling frequency was transmitted to enable the expander to track the gain adjustment applied by the compressor, even when the latter was limiting. Following successful trials with the BBC, in 1971 Pye TVT started to make and sell the S-i-S equipment under licence. The largest quantities went to the BBC itself, to the EBU and to Canada. Smaller numbers went to other countries including South Africa, Australia and Japan.Holder, J.E., Spenceley, N.M. and Clementson, C.S. (1984), ''A two channel sound in syncs transmission system'', IBC 1984, IEE Conference Publication No. 240, p. 345

Ruggedised S-i-S

A ruggedised version of the system was developed, which provided about 7

kHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or cycle) per second. The hertz is an SI derived unit whose formal expression in terms of SI base uni ...

audio bandwidth, for use over noisy or difficult microwave paths, such as those often encountered for

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Stereo S-i-S

Later systems, developed in the 1980s, used 14-bit linear PCM samples, digitally companded into 10-bit samples by means of NICAM-3

lossy compression In information technology, lossy compression or irreversible compression is the class of data compression methods that uses inexact approximations and partial data discarding to represent the content. These techniques are used to reduce data size ...

. These were capable of carrying two audio channels and were known as stereo Sound-in-Syncs.

ITV S-i-S

The ITV network used coders and encoders produced by RE of Denmark. The two variations of Sound-in-Syncs used by the BBC and ITV were not compatible. The terms DCSIS or DSIS was commonly used in ITV to describe dual channel Sound-in-Syncs. Very often material carried was not stereo, but dual mono.{{cite web , url=https://www.youtube.com/watch?v=l1xVgxmns90 , title=IBA Engineering Announcements - Graham Sawdy on NICAM - 20 March 1990 , website=

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