Digital cable

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Digital cable is the

standard, which was incompatible with existing analog cable systems.

In addition to providing

which occurred in analog systems.

History

In 1990,

In the 1990s, cable providers began to invest heavily in this new multi-channel digital TV technology to expand the number of channels and services available to subscribers. Increased competition and programming choices from

programming, digital music services, and high speed internet services. By 2000, most cable providers in the US were offering some form of digital cable TV to their customers.

Digital cable technology has allowed cable providers to compress video channels so that they take up less

error correction

to ensure the integrity of the received signal and uses a secure digital distribution system (i.e. a secure encrypted signal to prevent eavesdropping and theft of service.)

Most digital cable providers use

.

Channels

Digital cable technology can allow many TV channels to occupy the frequency space that would normally be occupied by a single analog cable TV channel. The number of channels placed on a single analog frequency depends on the compression used. Many cable providers are able to fit about 10 digital SD channels or 2 digital HD channels on a single analog channel frequency. Some providers are able to squeeze more channels onto a single frequency with higher compression, but often this can cause the video quality of the channel to degrade.[3]

The addition of this capability complicates the notion of a "channel" in digital cable (as well as in over-the-air

). The formal names for the two numbers that now identify a channel are the physical channel and the subchannel.

The physical channel is a number corresponding to a specific 6 MHz frequency range. See:

.

The

is a logical channel of data within the physical channel. Technically there can be up to 1024 subchannels in a physical channel, though in practice only a few are used (as the bandwidth must be divided among all the subchannels).

There are two ways providers try to make this easier for consumers. The first, accomplished through

, is where program and channel information is broadcast along with the video, allowing the consumer's decoder (set-top box or display) to automatically identify the many channels and subchannels.

The second (also accomplished through PSIP) is where, in an effort to hide subchannels entirely, many cable companies map virtual channel numbers to underlying physical and sub-channels. For example, a cable company might call channel 5-1 "channel 732" and channel 5-2 "channel 733". This also allows the cable company to change the frequency of a channel without changing what the customer sees as a channel number. In such arrangements, the physical/sub-channel numbers are called the "QAM channel", and the alternative channel designation is called the "mapped channel", "virtual channel", or simply "channel".

In theory, a set-top box can decode the PSIP information from every channel it receives and use that information to build the mapping between QAM channel and virtual channel. However, cable companies do not always reliably transmit PSIP information. Alternatively, CableCards receive the channel mapping and can communicate that to the set-top box.

The standard for signal transmission over digital cable television systems in the

boxes), high definition versions of local channels, and some cable channels are available.

Digital cable allows for the broadcast of

The

that delivers digital channels by satellite to small cable systems).

Digital cable channels typically are allocated above 552 MHz, the upper frequency of cable channel 78. (Cable channels above channel 13 are at lower frequencies than

North American cable television frequencies

.) Between 552 and 750 MHz, there is space for 33 6-MHz channels (231–396 SDTV channels); when going all the way to 864 MHz, there is space for 52 6-MHz channels (364–624 SDTV channels).

In the U.S., digital cable systems with 750 MHz or greater activated channel capacity are required to comply with a set of SCTE and CEA standards. Until September 4, 2020, these companies were also required to provide CableCARDs to customers that requested them.^[5]

• Cable Internet access
• Cable television in the United States
• CableCARD
• Digital television
• Direct-broadcast satellite
• DVB-C
• DigiCipher 2
• QAM Tuner
• Significantly viewed
• Tru2way

• National Cable and Telecommunications Association - Digital Cable
• Digital cable & Digital house
• US CATV Channels and Frequencies table (up to channel 78) Archived February 24, 2020, at the Wayback Machine
• US CATV Channels and Frequencies table (comprehensive)