One of the barriers I faced recently in building my MythTV-based HTPC (Home Theater PC) setup was understanding the terminology and acronyms in widespread use in the community. I wrote this hoping to document and illuminate some of the terms commonly in use.
- 120Hz: See 3:2 pulldown.
- 3:2 Pulldown: Television screens traditionally run at roughly 30 frames per second (60fps, but interlaced). Movies traditionally run at 24fps. Since both 60 and 30 are not divisible by 24, movies would display the same frame 3 times, then the next frame 2 times. This results in picture judder. Newer hi-def screens often have a mode to support 24fps movies by being capable of running at 48, 72, or 120fps, which are all multiples of 24. This is often referred to as “120Hz”; other modes are much less common.
- 5.1: Refers to sound systems with five channels. Center, right and left front speakers, right and left rear speakers, and a subwoofer channel composed of a mixed front right and front left signal.
- 7.1: Refers to sound systems with seven channels. Center, right and left front speakers, right and left middle speakers, right and left rear speakers, and a subwoofer channel composed of a mixed front right and front left signal.
- 480i: Old broadcast-quality television. 480 lines, interlaced.
- ATSC: A video standard widely in use in North America for high-definition broadcasting.
- DVI: Digital Video Interface. It is a digital signaling standard for PCs. This standard is virtually identical to HDMI video (and in fact converter cables are cheaply available), but treated differently by most screens.
- EIT: A standard to advertise show dates and programming schedules over ATSC.
- HDMI: Refers to the overscanned home-theater digital cabling standard. HDMI cables carry both digital audio and video on the same cable, and are capable of supporting 1080p resolutions. HDMI differs from DVI principally in that it uses overscan.
- HTPC: Home Theater PC. Usually an all-in-one, high-end PC with one or more video capture cards, a few terabytes of storage, a fast processor, and a good video card capable of projecting full-resolution native video on your screen.
- Interlaced: Refers to a technique of reducing the amount of data required by only displaying every-other-line on a display. The “i” or “p” on the end of a resolution description dicates whether it is “interlaced” or “progressive scan”. For instance, a given frame of a 480i broadcast is only 240 lines.
- IR Blaster: An infrared transmitter. Usually, this is set up on your HTPC to automatically change settings on a set-top box (STB) like DirectTV or a cable tuner.
- Judder or Screen Judder: A symptom where smooth-scrolling items like stock tickers or movie credits appear to run at inconsistent speeds. This is an artifact of 3:2 pulldown in some cases, but in other cases a firmware update to a screen or player may fix it. Not noticeable to many people.
- Just Scan: A Samsung-specific feature that will map an HDMI signal pixel-for-pixel rather than relying on overscan. Gives a cleaner picture at the expense of losing the extreme edges of the picture.
- Overscan: Sending a signal slightly larger than the expected resolution of the display device so that the signal takes up the full screen. This is usually used on analog devices rather than digital, since analog tolerances to display resolutions vary while digital usually maps pixel-for-pixel to the screen.
- Progressive Scan: Refers to resolution run at full resolution. For instance, a 480p signal transmits a full 480 lines per frame.
- NTSC: The North American 480i at 30 frames per second broadcast standard.
- VGA: Video Graphics Standard. Supports HD resolutions, but usually DVI will give a better picture. Many hi-def screens have VGA inputs for attaching a PC to the screen.