Digital Broadcasting arrives: the Analog Evolution

Introduction

The evolution of Canadian broadcasting from analog through to digital technology encompasses not simply home television sets. It also encompasses the transition to digital technology by television stations and networks, both in production and transmission, cable television and satellite distribution, in video and audio production, and in radio. The digital transition in broadcasting has paralleled the digital transition taking place in the rest of society, from home and business computer systems to telecommunications and satellite positioning systems.

The push to digital promised, and delivered, higher quality in both audio and video, and lower space requirements -- bandwidth -- for distribution. Digital technology changed both the way broadcast signals are sent out and the information those signals contain.

Analog vs. Digital

In the earliest days of broadcasting, analog signals were -- and in some areas, still are -- distributed over-the-air on a continuous carrier wave that extends outward from a transmitter until the signal fades out to nothing.

Digital signals are sent out off-air from a transmitter in digital - binary - bit streams but without any 'fade-out;' the signal is either there or not there.

The spectrum space required for analog television channels is substantially larger than for digital signals. The transition to digital therefore promised a potentially cost-saving reduction in bandwidth per channel for broadcasters, the capability of putting more channels in the same bandwidth space, and the use of analog spectrum for totally different - and for governments, lucrative - purposes. The switch to digital freed up precious spectrum space that brought in millions of dollars for governments who licensed bandwidth to other users.

Key Differences

There are three key differences between an analog and a digital image: 1) aspect ratio, 2) scan rate, and 3) resolution.

1) A conventional analog broadcast image, called NTSC (National Television Systems Committee) is presented in a 4:3 aspect ratio (width to height); a new digital image is most often in a 16:9 aspect ratio, more approximating the shape of a movie theatre screen.

2) Conventional NTSC is presented using what's called 'interlace' scan, where the image the camera sees is presented to the viewer as a set number of odd horizontal lines per second, followed by a set number of even horizontal lines per second totalling approximately 525 lines per second. Human vision fills in the picture, avoiding the appearance of flicker. Digital images can be either 'interlace' or the preferred 'progressive' scan, used in computer monitors, where the image is broken down and presented line-by-line sequentially to the viewer.

3) In terms of resolution, while a conventional NTSC image is 525-vertical interlaced lines, the highest definition digital signal is more than double that, at 1080 lines, presented in a progressive scan. A full HDTV image comprises about 1.2 gigabits of information.

The Road to Digital Broadcast

As early as the 1970s, the broadcast industry was working on experimental improved television and television images. In the early, 1980s, Sony developed and showcased an analog High Definition Television (HDTV) format, and in 1982, the United States formed the Advanced Television Systems Committee (ATSC), an industry consortium with international members, to research new TV formats.

The 1980s and the first half the 1990s saw highly-political debates about TV formats and the direction of new TV formats. At the same time, the spread of digitization in personal computers, home satellite television systems and the Internet propelled technology away from analog as the preferred advanced TV format and towards digital. Canada's Communications Research Centre together with CBC, hosted the first international High Definition Television Colloquium in Ottawa, in the mid-1980s, followed by HDTV Colloquia every two to three years. The Canadian group joined forces with European and Far East broadcasters, alternating conference sites between the three major areas until 1996.

The debates virtually ended in 1996, when the U.S. Federal Communications Commission (FCC) adopted the 18 related digital television formats of the ATSC Digital Television (DTV) Standard, called simply A53. A year later, in 1997, the Canadian government via Industry Canada adopted A53.

A53 defined digital television transmission and display formats, including both improved standard definition television (SDTV) and full High Definition television (HDTV). By 1998, the Spectrum Engineering Department of Industry Canada issued its spectrum allocation plan, assigning digital frequencies to Canadian broadcasters.

Canadian Digital Television Inc. (CDTV) was launched in the summer of 1998 in Ottawa by a cross-section of the Canadian broadcasting industry to begin co-ordinating the introduction of HDTV in Canada.

In 2002, the first application for high definition television programming was filed with the CRTC by CITY-TV in Toronto. The same year, Rogers Cable began distributing up to eight channels of high definition television including primarily the major U.S. stations. The first Canadian HDTV television station was Toronto's City-TV, which launched its new HD channel March 3, 2003.

Related Transitions

The A53 TV standard defined primarily over-the-air digital television transmission. In Canada, however, where the majority of the population had access to cable television, the issue of cable capacity became critical. Canadian cable companies began upgrading their 50 – 60 channel cable systems in the 1990s, moving to full digital and even part-fibre optic transmission systems. By about 2005, the majority of cable systems had 500-channel+ systems, capable of handling the entire existing broadcast universe, together with the parallel digital universe, slowly coming on stream.

In 1992, Telesat Canada began experiments with digital video compression over its satellite transmission system. The very first satellite-delivered digital television network in North America was Canada's own TMN - The Movie Network. TMN began digital satellite transmission, multiplexing its digital signal in 1992, providing TMN viewers with five movie channels using only one satellite television channel.

In radio, the Canadian broadcast regulator, the CRTC, approved a digital radio standard called Digital Audio Broadcasting, in 1995. Based on the European Eureka-147 radio standard, DAB required an eventual change-out of stations, transmission systems and radios, just as in digital television. Three years later, DAB radio licences were issued to a host of Canadian stations and DAB was fully operational in Toronto at the end of 1998, with 19 radio stations broadcasting in DAB off the CN tower.

Despite widespread European adoption of DAB, and Canadian implementation, the United States chose a different digital radio path, adopting IBOC -- In-Band On-Channel -- a system which fit digital signals into the existing analog spectrum, together with new digital satellite radio systems. Both technology and politics combined to slow and then halt DAB, at least in Canada. Ten years later, the two U.S. digital satellite radio companies had both launched services in Canada with Canadian partners, and both were undergoing continental mergers.

Costs of Digital

The costs of the transition to digital television have been enormous. A basic estimate of the costs prior to the transition included such figures as: $750,000. to $1 million per transmitter, with over 1,000 private transmitters located across the country - for transmission alone; for a single television station, it was estimated to cost about $3 million to change-over to digital. In 1998, the cable industry estimated their costs at about $900 million, to change-over to digital technology. By comparison, the U.S. public network PBS, the first North American network to change over its entire system, planned its digital conversion before 2000, with a ballpark cost of $1.7 billion.

For consumers, the entry-level cost for an HDTV set in the early years of 1998 -- 2000 was about $10 -- 12,000. Ten years later, those costs had dropped to $500 - $1,000 depending on size, approximating the end-of-days previous cost of the analog NTSC systems.

Current State of Affairs (at October 2009)

The shut-off date for analog television was originally 2006, in the U.S. and 2007, in Canada. Both deadlines, however, were delayed. The U.S. completed the transition to digital television in 2009, and on June 12, 2009, that country closed down its analog NTSC television system. By that date, most Canadian networks and many stations had implemented digital and/or HDTV signal transmission, but the official shut-down of the analog system in Canada remained scheduled for 2011.

Meantime, the country's slow economic recovery significantly slowed down the rate of implementation of digital signals at the station level.

Daphne Lavers - October, 2009

 


Glossary

AC-3

Audio Standard: the ATSC-approved 5.1 channel digital audio format for HDTV, now called Dolby Digital (using approximately 13:1 compression for six discreet audio channels - left, centre, right, left rear, right rear, and sub-woofer)

analog

a method of delivering television programs or radio signals by radio frequency carrier waves, varying the voltage in an electric signal; the carrier waves transmit outward from the transmitter becoming weaker with distance, until the signal fades away to nothing; analog television channels in North American were broadcast using the NTSC (National Television Systems Committee) 525-line format

ATSC

Advanced Television Systems Committee (U.S.) American industry consortium founded in 1982 to examine new forms of television broadcasting; originators of the 'A53' television standard

ATSC-53 – A53

the standards document developed by the Advanced Television Systems Committee and adopted by the Federal Communications Commission (U.S.) which defines 18 display formats for high definition and digital television; originally titled ATSC53, numbered simply according to the sequential document numbering system adopted by ATSC, and shortened to A53

bandwidth

a measure of the amount of frequency spectrum occupied by a signal; usually measured in Hertz (Hz), Kilohertz (KHz) or Megahertz (MHz); a single analog television channel has 6 Meg. bandwidth, but that same 6 Meg. bandwidth can contain far more television channels in digital format when used with video compression

baud

named after a French engineer, Jean-Maurice-Emile Baudot, baud was first used to measure the speed of telegraph transmissions; one baud is one electronic state change per second; it became a common measure for data transmission speed until replaced by the more accurate bps - bits per second

binary

a mathematical set or language using only two characters - bits - or states e.g. on and off, as opposed to a standard set or language, for example metric, which uses a base of 10

bit

binary digit

compression

reduction in size of digital data files - video, audio, voice or data - by the removal of redundant and/or non-critical information; HDTV signals are now routinely compressed to 19.5 Meg/sec. for transmission

DAB

Digital Audio Broadcasting; a digital radio format adopted in Canada operating in a 40 Megahertz allocation of L-band; DAB radio covers the full range of human hearing, from 5 - 20,000 Hertz; it was seen as a replacement radio service for current AM and FM and has been implemented in Europe

digital

a system of communication that uses a stream of bits or discreet quantities to represent the signal

Eureka 147

an international consortium of broadcasters, network operators, consumer electronic industries and research institutes who collaborated to develop the DAB digital radio standard, implemented in various parts of the world

gigabit

one billion bits (of data)

GHz

Gigahertz; one billion hertz, or one billion cycles per second, in the frequency spectrum for RF communications; satellites operate in the GHZ frequency band

IBOC

In-band On-Channel; a digital radio system format adopted in the United States, which places digital radio frequencies within existing AM and FM frequencies, seen as a competitive or additional radio service

Interlace (scan)

(video) an electronic image scanning format, used by standard NTSC television sets where a set number of odd horizontal lines per second are presented, rapidly followed by a set number of even horizontal lines per second; human vision fills in the picture, avoiding the appearance of flicker

NTSC

National Television Systems Committee (U.S.) which defined the original 525-line analog television format

Progressive (scan)

an electronic image scanning system which scans and presents each line of an image sequentially to a viewer; used in computer images and in high definition television systems

spectrum

the entire range of wavelengths of electromagnetic radiation: frequencies in the electromagnetic spectrum between 100 KHz and 100 GHz

 


ATSC 53 Television Display Standards

 

Resolution
Horizontal x Vertical
Pixels

Aspect
Ratio

Picture
Rate

Scanning

 

High
Definition
Television

1080x1920

16x9

24
30
60

Progressive
Progressive
Interlaced

720x1280

16x9

24
30
60

Progressive
Progressive
Progressive

 

Standard
Definition
Television

480x704

16x9

24
30
60
30

Progressive
Progressive
Progressive
Interlaced

480x704

4x3

24
30
60
30

Progressive
Progressive
Progressive
Interlaced

480x640

4x3

24
30
60
30

Progressive
Progressive
Progressive
Interlaced

 

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