TV Standard Note

Incompatible Broadcast Standards

A TV program produced in one country can't automatically be viewed in many other countries without converting it to a different technical standard. These technical differences relate to both incompatibilities in equipment and in the approach to broadcasting the audio and video signals.

Some 14 different SDTV  (standard definition) broadcast TV standards have been used at different times throughout the world. They can be reduced to three primary groups:

• NTSC (National Television System Committee)
• SECAM (Sequential Color and Memory)
• PAL (Phase Alternating Line)

Within these there are two major differences:

• the total number of horizontal lines in the picture (525 or 625 for standard definition or SDTV) and 1,125 and 1,250 for high-definition TV (HDTV)
   
• whether the transmission rate is 25 or 30 frames (complete pictures) per-second 

Aspect Ratios

Although the number of scanning lines may have varied, until recently all television systems had a 4:3 aspect ratio. The aspect ratio is the width-height proportion of the picture.

The 4:3 ratio (note red box in the photo on the right) was consistent with motion pictures that predated the wide screen aspect ratios used in CinemaScope, VistaVision, and Panavision. When the HDTV standard was introduced it also made use of this wider (generally, 16:9) aspect ratio.

In the picture here, the wider area (just inside the blue borders) represents the 16:9 ratio used in HDTV. Compared to the 4:3 ratio, this aspect ratio conforms to the wider perspective of normal human vision.


Major Microphone Designs

 There are six common microphone designs:

• hand held -- the type held by on-camera talent or used for on-location interviews
  
• personal mic (lavaliere / clip-on mic) -- Whether hung from a cord around the neck (lavaliere) or clipped to clothing, these are all referred to as personal mics.
  
• shotgun -- used for on-location production to pick up sounds a moderate distance from the camera
  
• boundary effect microphone -- also called PZ or PZM mics These rely primarily on reflected sounds from a hard surface such as a tabletop
  
• contact mics -- which pick up sound by being in direct physical contact with the sound source. These mics are generally mounted on musical instruments.
  
• studio microphones -- the largest category of microphone. These include a number of application designs that we'll discuss.

These six categories include different transducer types, or approaches to converting sound waves into electrical energy. 

Directional Characteristics

In an earlier module we talked about the angle of view of lenses -- the area that a lens "sees." Microphones have a similar attribute: their directional characteristics, or, you might say, the angle of view that they "hear."

In microphones there are three basic directional categories:

• omnidirectional
• bi-directional
• unidirectional