Questions regarding Upconversion are pretty frequent on this site. Here's a summary which provides a few "rules of thumb", however, please realize that, as with all rules of thumb, there will be exceptions.
Upconversion is a term that can apply to "deinterlacing" (taking a 480i signal and making it 480P) or any "bettering" of the signal say 480i to 1080i)
1. Upconversion in a STB (Set top box):
STBs are usually the worst place to do upconversion, so if the STB allows you to "passthrough" the signal (sometimes called native) or to set 480i as the output format for SD channels, while allowing 1080i (or 720P and 1080i passthrough) for HD channels, that is usually your best option.
Most recent STBs do a pretty good job of upconversion and setting the STB to 1080i-Fixed (only) will often avoid some hiccups that occur with HDMI connections, as well as speedier channel changes when channels of different format are involved.
Some STBs (BTV, Fibe, Rogers RTN Firmware, etc) do not allow for native/passthrough option, so feel free to experiment with the various output formats, although since BTV/Fibe converts all HD channels to 720P, 720P is usually the better option there. For other (non-Bell) providers, the better option is usually 1080i. If the STB has a 1080P option, you can try that too. If you have a 4K TV, you can set the output to 4K.
(On some STBs (SA, *C), the "native/passthrough" mode produces a bit more overscan than a single setting like 1080i)
2. Upconversion in Upconverting and HD DVD players:
If you have an upconverting DVD player, then by all means use it to perform the upconversion of SD DVDs to 720P, 1080i or 1080P depending on the TV's capabilities. Most TVs seem to prefer a 1080i (or 1080P if available) signal, however, feel free to experiment with the various formats to see what looks best to you. An HDMI connection is required for upconversion as the component video port is limited to 480P for commercial SD DVDs.
The reason that the upconversion in DVD players seems to do such a good job seems to be that it's done in the digital domain and very close to the source material. If you have a 4K player and 4K TV, use that.
3. Upconversion in TVs.
Most TVs do good upconversion, so, except for upconverting DVD players, it's usually best to pass the original signal through to the TV for final conversion to the native display format, as unaffected as possible, unless you encounter issues due to this sort of setting (usually with HDMI connections)
4. Upconversion in AVRs (AV Receivers):
A lot of the newer AVRs will allow you to upconvert incoming signals, however, there are caveats.
- not all types of signals are upconverted.
- not all formats are upconverted.
- you'll need to carefully check your operating manual as to what is and isn't upconverted.
- most AVRs do not upconvert HDMI signals - they are passed to the TV, untouched.
Most times the TV will do a better job than the AVR, so we usually recommend that you pass the signal unaffected to the TV, but again, feel free to experiment. The more expensive the AVR, the more likely there may be a positive effect (and vice versa)
5. Upconversion by the Affiliate.
Since they have expensive equipment instead of a chip that may cost a few dollars, the upconversion done by an affiliate for an HD channel is almost always superior to what can be done by a TV or STB.
A quick note to Plasma/CRT owners - if you wish to have the TV have separate stretch modes for SD and HD signals, then you would not want upconversion done by the AVR, since it would preclude that (automatic) option (unless the AVR does the appropriate stretching) - this is mostly with regard to STBs.
A word on transcoding:
Do not confuse upconversion and transcoding. Many newer AVRs also transcode incoming signals - say composite or component video signals may be transcoded to HDMI for a single connection to the TV. (be aware that this may not be your best option because this then precludes optimizing the individual inputs/components on the TV for optimum picture quality. Many new TVs can be optimized for each component/input, so if you have only one connection, this is not possible.
For information on TV formats, see:
FAQ - Native Display Resolution vs. Input Format - Canadian TV, Computing and Home Theatre Forums
Limitations due to connections:
BD players and upconverting players are usually limited to 480P when using the component video connection for standard
(480i) DVDs. No such limit exists when using HDMI.
Please PM me if you have suggestions for this FAQ.