What Does it Mean?
The 480i means that the signal carries 480 horizontal lines of information, the i is for interlaced, meaning each line is refreshed alternately. The 1080 is for the lines, i is for interlaced, but the p is for progressive, which means the lines refresh from the top down. HDTV come in two varieties, 1080i and 1080p. Currently the 1080p sets have an advantage in picture quality over the 1080i ones.
The frequency doesn’t make too much difference to picture quality as it is cleaned up by the set-top box or TV. The refresh rate of the TV is what makes the most difference to the quality of a picture.
When looking at the specifications of a TV, you will often see “60Hz" or “120Hz" in the description. This is entirely different to frequency, this is the refresh rate.
A refresh rate of 100Hz is how many times a second an image frame is drawn on the screen. For example, a movie is broadcast at 24Hz, which is 24 frames per second. A 60Hz LCD TV will convert the frames into 30Hz frames automatically, and refresh them twice every second. A 120Hz TV will repeat the original 24Hz frame five times within every 24th of a second.
In the real world what this means is that a 120Hz TV will produce a much clearer, crisper picture than that of a 60Hz one because the image is being refresh twice as quickly. Moving images will appear sharper and with less flickering than a 60Hz picture and will have much less motion blur.