The primary frequencies associated with the color information in composite video signals, based on common standards like NTSC and PAL, are 3.58 MHz for NTSC and 4.43 MHz for PAL. These frequencies relate specifically to the color subcarrier signal, a crucial component within the overall composite video structure.
Understanding Composite Video Frequencies
A composite video signal is a complex waveform that combines several components necessary for displaying an image on older television sets and monitors. These components include:
- Luminance (Y): Carries the black and white (brightness) information. This occupies a broad range of frequencies.
- Chrominance (C): Carries the color (hue and saturation) information. This is modulated onto a specific subcarrier frequency.
- Synchronization (Sync): Pulses that define the start and end of lines and frames, ensuring the image is drawn correctly on the screen.
While the entire signal occupies a certain bandwidth, the question often refers to key characteristic frequencies, particularly the color subcarrier frequency, as it's fundamental to decoding the color part of the signal.
Key Frequencies Mentioned in the Reference
The provided reference highlights the color-related frequencies for the two most prevalent analog composite video standards: NTSC and PAL.
NTSC Composite Video Frequency
For the NTSC standard, primarily used in North America and parts of South America and Asia, the reference states:
"In NTSC composite video, the 3.58 MHz burst signal is inverted in phase (180° out of phase) from the reference subcarrier."
The 3.58 MHz refers to the frequency of the color subcarrier, often more precisely stated as 3.579545 MHz. The "burst signal" is a small sample of this frequency transmitted during the horizontal blanking interval. Its purpose is to provide the receiver with a phase and amplitude reference to decode the color information correctly.
PAL Composite Video Frequency
For the PAL standard, common in Europe, Australia, and parts of Asia and Africa, the reference notes:
"In PAL, the phase of the 4.43 MHz color subcarrier alternates on successive lines."
The 4.43 MHz refers to the frequency of the color subcarrier used in the PAL system, specifically the PAL-B/G/H/I/N variants. This frequency is approximately 4.43361875 MHz. The PAL system's characteristic alternating phase of the color subcarrier on successive lines helps to reduce color errors.
Summary Table
| Standard | Region(s) Primarily Used | Color Subcarrier / Burst Frequency |
|---|---|---|
| NTSC | North America, parts of Asia | 3.58 MHz (approx. 3.579545 MHz) |
| PAL | Europe, Australia, parts of Asia/Africa | 4.43 MHz (approx. 4.43361875 MHz) |
These frequencies are critical for a display device to separate the color information from the brightness information and accurately reproduce the intended colors.
