Well, you can check the stretch modes on your TV and on the STB. You can press the * button on the STB remote repeatedly to run through the stretch modes and I assume there's a similar function on the TV. See the following FAQs:
http://www.digitalhome.ca/forum/showthread.php?t=76074 Stretch Modes
http://www.digitalhome.ca/forum/showthread.php?t=76089 Black Bars
http://www.digitalhome.ca/forum/showthread.php?t=57741 Useful post.
I find it useful to go to a channel like CP24. Unstretched this should be a 4:3 channel with no distortion and no missing information. As you run through the various stretch modes, you can see what happens to the information/boxes, etc.
http://www.digitalhome.ca/forum/showthread.php?t=76074 Stretch Modes
http://www.digitalhome.ca/forum/showthread.php?t=76089 Black Bars
http://www.digitalhome.ca/forum/showthread.php?t=57741 Useful post.
I find it useful to go to a channel like CP24. Unstretched this should be a 4:3 channel with no distortion and no missing information. As you run through the various stretch modes, you can see what happens to the information/boxes, etc.