Understanding digital cable
From LinuxMCE wiki
In the United States, a transition to digital cable is being made on June 12, 2009
February 17th, 2009. Many sources have been giving confusing information about who will need converters and this also affects LMCE's tv recording. Here are the answers that LMCE users will need to know about the switch. Other countries will have different schedules for converting terrestrial, cable and satellite services.
OTA: This is shorthand for "Over the Air". This refers to any tv channels which are broadcast for free. They are over the air in the sense that all you need is an antenna plugged into your tv to access them. There is no need for a subscription to a cable company in order to receive these stations. However, some cable companies also provide these channels in their tv line up. For example, NBC can be tuned using rabbit ears, but also comes included in most Comcast packages.
Broadcast Television: This is the another way to say OTA. As are Digital Terrestrial Television, or DTT.
A Coax cable: This is the standard tv cable. When going from a wall jack to the tv, you use a coax cable. It's basically an insulated piece of copper wiring with an attachment on the ends to hold it in the plug.
Analog cable: This refers to the type of signal that comes through the coax cable. It is very similar to a radio signal in that multiple channels (or stations) can be carried through the wire on different frequencies. You don't need a wire for each tv station. This is why we use the term "tv tuner". A tuner is able to lock onto different frequencies carried through the coax cable. This is simplified definition. If you have any more details, please add them.
Digital cable: This also refers to the type of signal that comes through a coax cable. But with digital tv, 1s and 0s are sent through the coax cable. Thus, a different type of tuner is required to understand this stream of data.
NTSC: National Television System Committee. The analogue television standard used for North America and some other countries. It is actually a system for encoding the colour signal. Although it doesn't necessarily mean 60Hz refresh rate, this is usually implied because of the local power frequencies in most countries that use it. It is used for transmitting analogue television both terrestrially (broadcast to your antenna) and over cable networks and satellite. Compare: PAL
PAL: Phase Alternate Line. The analogue television standard used for much of the world outside North America. It is actually a system for encoding the colour signal. Although it doesn't necessarily mean 50Hz refresh rate, this is usually implied because of the local power frequencies in most countries that use it. It is used for transmitting analogue television both terrestrially (broadcast to your antenna) and over cable networks and satellite. Compare: NTSC
ATSC: Advanced Television Systems Committee. The digital replacement for NTSC - used in much the same territories. Although some digital satellite services in the North American territory, at least, have opted to use DVB-S/DVB-S2 instead - this is the digital replacement for PAL in satellite services. eg. Dish.
DVB: Digital Video Broadcasting. The digital replacement for PAL - used in much the same territories. DVB-S, DVB-T, DVB-C, DVB-H refer to the specific standards for Satellite, Terrestrial, Cable and Handheld, respectively. There are additional formats already in place or to be released soon that include version 2's of these existing formats.
QAM: Quadrature Amplitude Modulation is a format that can be used for digital information. Just like there are multiple types of file formats for an audio file, (mp3, wma, ogg, flac, etc) there are formats for digital television. QAM seems to be becoming the standard format in the US. More information is needed here, so please help out.
Encrypted signal: If a piece of data is encrypted, that means that the information is sent in code which only a few people are allowed to know. Cable companies often encrypt their cable signal in order to prevent stealing. If the signal cannot be decrypted, the tv signal is not viewable.
Clear QAM: Clear QAM is basically a television signal in QAM format that is not encrypted. Virtually all of the OTA digital stations in the U.S.A use this format.
The switch to digital
Analogue Switch Off (ASO) So what exactly will be happening on June 12, 2009
February 17th? All OTA stations will be required by federal law to cease broadcasting analog and begin broadcasting digital. That means that the free stations which are tuned using rabbit ears will no longer carry an analog signal. They will carry digital. Thus, a digital tuner will be needed to understand this new stream of data.
However, cable companies are NOT required to change to digital. Hence, comcast customers will not be required to change anything once the
February 17th change happens. Comcast will still continue to send analog cable to it's subscribers if they so choose. Here are some common situations and what the outcome will be after February 17th ASO.
Cable subscription: NO, I use an antenna
Does your tv have a digital tuner?: NO
Result: In order to continue watching any television at all, you will need a digital converter. Your antenna will be plugged into the converter box, which will then feed into your tv set.
Cable subscription: Yes, from Comcast (or any other)
Analog or digital subscription?: Analog
Does your tv have a digital tuner?: NO or YES. Doesn't matter either way
Result: Nothing will need to change. Your cable provider will continue providing you with analog tv and your television will be able to understand it. Comcast has specifically said it will continue broadcasting analog.
Cable subscription: Yes, from Comast (or any other)
Analog or digital subscription?: Digital and/or High Def
Does your tv have a digital tuner?: Yes, of course
Result: Nothing will change for you either. You already are using digital, so the change doesn't affect you.
Cable subscription: Yes, from a satellite provider
Analog or digital subscription?: either
Result: Satellite TV will not be affected in anyway by the change to digital.
What does it mean for LMCE users?
First and foremost, it is essential that your tuner first be compatible with LMCE. Before asking the question "Will I be able to record my television?", you must first ask "Will my tuner work at all with LMCE?" For that, please check the wiki section on tuner cards.
Now, onto business. The ability of your computer's tv tuner will be limited by the type of signal. If you have an analog cable subscription, LMCE will be able to tune every single channel which you enjoy on your normal television. You will need an NTSC capable tuner for your computer.
The problems arise when trying to record digital television. In general, most, if not all cable companies encrypt their digital tv signals. Since they undoubtedly keep their encryption techniques a secret, LMCE will be unable to decrypt those signals. The net result is that digital cable from a provider is unable to be tuned/recorded by LMCE, even when using a digital (ATSC) tuner. The only exceptions are the free, OTA channels. These channels are not encrypted, thus your ATSC computer tuner will be able to watch these streams. There are work arounds to recording digital subscriptions, but that will be added later as it is very cumbersome and unreliable.