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

Analog television is the analog transmission that involves the broadcasting of encoded analog audio and analog video signal: one in which the message conveyed by the broadcast signal is a function of deliberate variations in the amplitude and/or frequency of the signal...

 waveform. This is used on point-to-point links within broadcasting networks, including studio/transmitter link

Studio/transmitter link

A studio-transmitter link sends a radio station's or television station's audio and video from the broadcast studio to a radio transmitter or television transmitter in another location....

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

Pulse-code modulation is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, Compact Disc and DVD formats, as well as other uses such as digital telephone systems...

 (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 and offered improved sound quality and reliability.

Awards

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

• The Royal Television Society
  Royal Television Society
  The Royal Television Society 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...
  
  's Geoffrey Parr Award in 1972
• A Queen's Award for Enterprise in 1974
• In 1999, a Technology & Engineering Emmy Award
  Technology & Engineering Emmy Award
  A Technology and Engineering Emmy Award is given by the National Academy of Television Arts and Sciences for outstanding achievement in technical or engineering development...
  
  

Original mono S-i-S

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

Ruggedised S-i-S

A ruggedised version of the system was developed, which provided about 7 kHz audio bandwidth, for use over noisy or difficult microwave paths, such as those often encountered for outside broadcasts.

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

NICAM

Near Instantaneous Companded Audio Multiplex is an early form of lossy compression for digital audio. It was originally developed in the early 1970s for point-to-point links within broadcasting networks...

lossy compression. 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 compatabile. The terms DCSIS or DSIS was commonly used in ITV to describe dual channel Sound-in-Syncs. Very often material carried was dual mono and not stereo.

Further reading

• Waveform Specification of the BBC Sound-in-Syncs Equipment, EBU Review, 121A, June 1970.
• Chorley, J.M. and Shorter, D.E.L. (1970), P.C.M. Sound-in-Syncs: Operational Systems for Video Distribution and Contribution Networks, IEE Conference Publication, No. 69, 1970 International Broadcasting Convention
• Dalton, C.J. (1968), The Distribution of Television Sound Signals by PCM Signals incorporated in the Vision Waveform, IEE International Broadcasting Convention, September 1968, Vol. 46, Part 1
• Sanders, J.R. (1967), Pulse sound: a system of television sound broadcasting using pulses in the video waveform, BBC Engineering Monograph, No. 67, May 1967
• Sanders, J.R. (1968) Pulse-code modulation for high-quality sound signal distribution: Incorporation of the sound signal in the video signal. BBC Research Department report (PDF)
• Shorter, D.E.L., Chew, J.R., Howarth, D. and Sanders, J.R. (1968), Pulse code modulation for high-quality sound signal distribution, BBC Engineering Monograph, No. 75, December 1968
• Shorter, D.E.L. (1969), The Distribution of Television Sound by Pulse-code Modulation Signals incorporated in the Video Waveform, EBU Review, No. 113A, February 1969