Digital cable technology can acquiesce abounding TV channels to absorb the abundance amplitude that would commonly be active by a individual analog cable TV channel. The amount of channels placed on a individual analog abundance depends on the compression used. Abounding cable providers are able to fit about 10 agenda SD channels or 2 agenda HD channels on a individual analog approach frequency. Some providers are able to clasp added channels assimilate a individual abundance with college compression, but generally this can could cause the video superior of the approach to degrade.
The accession of this adequacy complicates the angle of a "channel" in agenda cable (as able-bodied as in over-the-air ATSC agenda broadcasts). The academic names for the two numbers that now analyze a approach are the concrete approach and the subchannel.
The concrete approach is a amount agnate to a specific 6 MHz abundance range. See: North American cable television frequencies.
The subchannel is a analytic approach of abstracts aural the concrete channel. Technically there can be up to 1024 subchannels in a concrete channel, admitting in convenance alone a few are acclimated (since the bandwidth have to be disconnected a part of all the subchannels).
There are two means providers try to accomplish this easier for consumers. The first, able through PSIP, is area affairs and approach advice is advertisement forth with the video, acceptance the consumer's decoder (set-top box or display) to automatically analyze the abounding channels and subchannels.
The additional (also able through PSIP) is where, in an accomplishment to adumbrate subchannels entirely, abounding cable companies map basic approach numbers to basal concrete and sub-channels. For example, a cable aggregation ability alarm approach 5-1 "channel 732" and approach 5-2 "channel 733". This aswell allows the cable aggregation to change the abundance of a approach after alteration what the chump sees as a approach number. In such arrangements, the physical/sub-channel numbers are alleged the "QAM channel", and the another approach appellation is alleged the "mapped channel", "virtual channel", or artlessly "channel".
In theory, a set-top box can break the PSIP advice from every approach it receives and use that advice to body the mapping amid QAM approach and basic channel. However, cable companies do not consistently anxiously address PSIP information. Alternatively, CableCards accept the approach mapping and can acquaint that to the set-top box.
The accession of this adequacy complicates the angle of a "channel" in agenda cable (as able-bodied as in over-the-air ATSC agenda broadcasts). The academic names for the two numbers that now analyze a approach are the concrete approach and the subchannel.
The concrete approach is a amount agnate to a specific 6 MHz abundance range. See: North American cable television frequencies.
The subchannel is a analytic approach of abstracts aural the concrete channel. Technically there can be up to 1024 subchannels in a concrete channel, admitting in convenance alone a few are acclimated (since the bandwidth have to be disconnected a part of all the subchannels).
There are two means providers try to accomplish this easier for consumers. The first, able through PSIP, is area affairs and approach advice is advertisement forth with the video, acceptance the consumer's decoder (set-top box or display) to automatically analyze the abounding channels and subchannels.
The additional (also able through PSIP) is where, in an accomplishment to adumbrate subchannels entirely, abounding cable companies map basic approach numbers to basal concrete and sub-channels. For example, a cable aggregation ability alarm approach 5-1 "channel 732" and approach 5-2 "channel 733". This aswell allows the cable aggregation to change the abundance of a approach after alteration what the chump sees as a approach number. In such arrangements, the physical/sub-channel numbers are alleged the "QAM channel", and the another approach appellation is alleged the "mapped channel", "virtual channel", or artlessly "channel".
In theory, a set-top box can break the PSIP advice from every approach it receives and use that advice to body the mapping amid QAM approach and basic channel. However, cable companies do not consistently anxiously address PSIP information. Alternatively, CableCards accept the approach mapping and can acquaint that to the set-top box.
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