Colorburst
The Anome moved page Colorburst to Color burst over redirect it's "color burst" not "colorburst"
New page
{{Short description|Synchronisation signal in colour video}}
{{For|the instant camera range|Kodak Colorburst}}
{{Refimprove|date=September 2014}}
[[File:Commodore 64 PAL horizontal sync and colourburst.jpg|200px|right|thumb|Horizontal sync and color burst of the composite output of a [[Commodore 64]] computer]]
The '''color burst''' is one part of the composite sync used in analog television signals. It consists of a "packet" of the sine wave chroma subcarrier and is used as a reference to decode color information in the video. By synchronizing an [[Electronic oscillator|oscillator]] with the color burst at the [[Analog television#Structure of a video signal|back porch]] (beginning) of each [[scan line]], a television receiver is able to restore the suppressed carrier of the [[chrominance]] (color) signals, and in turn decode the color information.
== Explanation ==
In [[NTSC]], the color burst frequency is exactly 315/88 = 3.579{{overline|54}}{{efn|name=repeating decimal|[[Repeating decimal#Notation|Repeating decimal notation]]}} [[MHz]] with a phase of 180°. [[PAL]] uses a frequency of exactly 4.43361875 MHz, with its phase alternating between 135° and 225° from line to line. Since the color burst signal has a known amplitude, it is sometimes used as a reference level when compensating for amplitude variations in the overall signal.
[[SECAM]] is unique in not having a color burst signal, since the chrominance signals are encoded using [[Frequency modulation|FM]] rather than [[QAM]], thus the signal phase is immaterial and no reference point is needed.
== Rationale for NTSC Color burst frequency ==
{{Details|NTSC#Color encoding}}
The original black and white NTSC television standard specified a frame rate of 30 Hz and 525 lines per frame, or 15750 lines per second. The audio was frequency modulated 4.5 MHz above the video signal. Because this was black and white, the video consisted only of luminance (brightness) information. Although all of the space in between was occupied, the line-based nature of the video information meant that the luminance data was not spread uniformly across the [[frequency domain]]; it was concentrated at multiples of the line rate. Plotting the video signal on a [[spectrogram]] gave a signature that looked like the teeth of a comb or a gear, rather than smooth and uniform.
[[RCA Corporation|RCA]] discovered{{cite journal |last=Brown and Luck|date=June 1953 |title=Principles and development of color television systems |url=http://www.americanradiohistory.com/ARCHIVE-RCA/RCA-Review/RCA-Review-1953-June.pdf |journal=RCA Review |volume=XIV |pages=155–156}} that if the [[chrominance]] (color) information, which had a similar spectrum, was modulated on a carrier that was a [[half-integer]] multiple of the line rate, its signal peaks would fit neatly between the peaks of the luminance data and interference was minimized. It was not eliminated, but what remained was not readily apparent to human eyes. (Modern televisions attempt to reduce this interference further using a [[comb filter]].)
To provide sufficient bandwidth for the chrominance signal, yet interfere only with the highest-frequency (and thus least perceptible) portions of the luminance signal, a chrominance subcarrier near 3.6 MHz was desirable. 227.5 = 455/2 times the line rate was close to the right number, and 455's small factors (5 × 7 × 13) make a divider easy to construct.
However, additional interference could come from the [[audio signal]]. To minimize interference there, it was similarly desirable to make the distance between the chrominance [[carrier frequency]] and the audio carrier frequency a half-integer multiple of the line rate. The sum of these two half-integers implies that the distance between the frequency of the luminance carrier and audio carrier must be an integer multiple of the line rate. However, the original NTSC standard, with a 4.5 MHz carrier spacing and a 15750 Hz line rate, did not meet this requirement: the audio was 285.714 times the line rate.
While existing black and white receivers could not decode a signal with a different audio carrier frequency, they could easily use the copious timing information in the video signal to decode a slightly slower line rate. Thus, the new color television standard reduced the line rate by a factor of 1.001 to 1/286 of the 4.5 MHz audio subcarrier frequency, or about 15734.2657 Hz. This reduced the frame rate to 30/1.001 ≈ 29.9700 Hz, and placed the color subcarrier at 227.5/286 = 455/572 = 35/44 of the 4.5 MHz audio subcarrier.{{cite web |url=https://www.antiqueradio.org/art/NTSC%20Signal%20Specifications.pdf |title=NTSC Signal Specifications |date=23 May 2018 |website=Antique Radio.org}}
== Crystals ==
An NTSC or PAL television's color decoder contains a color burst [[crystal oscillator]].
Because so many analog color TVs were produced from the 1960s to the early 2000s, [[economies of scale]] drove down the cost of color burst crystals, so they were often used in various other applications, such as [[Electronic oscillator|oscillators]] for [[microprocessor]]s or for [[amateur radio]]: 3.5795 MHz has since become a common [[QRP operation|QRP]] calling frequency in the [[80-meter band]], and its [[frequency multiplier|doubled]] frequency of 7.159 MHz is a common calling frequency in the [[40-meter band]]. Tripling this frequency is also how [[FM radio]] circuits came to use a nominally 10.7 MHz [[intermediate frequency]] in [[Superheterodyne transmitter|superheterodyne]] conversion.
{{Table alignment}}
{| class="wikitable sortable col3center"
|+ Non-television uses of NTSC color burst frequency
(generally only in the NTSC version of each device):
''f'' = 315 MHz/88 = 3.579{{overline|54}}{{efn|name=repeating decimal}} MHz
! Component
! Frequency
! Ratio
|-
| [[Intellivision]] CPU
| rowspan="2" | 0.8949 MHz
| rowspan="2" | {{sfrac|4}}''f''
|-
| [[TRS-80 Color Computer]] CPU (normal speed)
|-
| [[Apple II]] CPU (short cycles only, one in 65 cycles is longer)
| rowspan="4" | 1.0227 MHz
| rowspan="4" | {{sfrac|2|7}}''f''
|-
| [[VIC-20]] CPU
|-
| [[Commodore 64]] CPU
|-
| [[Commodore 128]] CPU (SLOW & [[C64]] compatible modes)
|-
| [[Atari 2600]] CPU Atari 2600 Specifications http://problemkaputt.de/2k6specs.htm
| rowspan="2" | 1.1932 MHz
| rowspan="2" | {{sfrac|3}}''f''
|-
| [[Intel 8253]] interval timer in IBM PC (remains in use {{As of|2008|alt=today}})
|-
| [[Fairchild Video Entertainment System]] CPU
| rowspan="6" | 1.7898 MHz
| rowspan="6" | {{sfrac|2}}''f''
|-
| [[Odyssey 2]] CPU
|-
| [[Atari 8-bit computers]]{{cite book |title=Altirra Hardware Reference Manual |chapter=3.3 Cycle Timings |page=43 |first=Avery |last=Lee |date=2024-09-21 |access-date=2024-11-27 |url=http://www.virtualdub.org/downloads/Altirra%20Hardware%20Reference%20Manual.pdf#page=43}} and [[Atari 7800]] CPU
|-
| [[Plus/4]] CPU
|-
| [[Nintendo Entertainment System]] CPU
|-
| [[TRS-80 Color Computer#Color Computer 3 (1986%E2%80%931991)|TRS-80 Color Computer 3]] CPU (fast mode)
|-
| [[Commodore 128]] CPU (FAST & CP/M modes)
| 2.0454 MHz
| {{sfrac|4|7}}''f''
|-
| rowspan="2" | [[Super NES]] CPU
| 2.6847 MHz
| {{sfrac|3|4}}''f''
|-
| rowspan="7" | 3.5795 MHz
| style="text-align:center" | ''f''
|-
| [[Master System]] CPU
| rowspan="6" style="text-align:center" | ''f''
|-
| [[MSX]] CPU
|-
| [[Amateur radio]] Tx/Rx crystal for 80m band
|-
| [[ColecoVision]] CPU
|-
| [[Yamaha OPL|Yamaha OPL and OPL2]] FM synthesis sound chips
|-
| [[ACPI]] power management timer
|-
| [[IBM Personal Computer]] 5150 CPU
| 4.7727 MHz
| {{sfrac|4|3}}''f''
|-
| [[Amiga]] CPU
| rowspan="5" | 7.1591 MHz
| rowspan="5" | 2''f''
|-
| [[Tandy 1000#Tandy 1000 TX and Tandy 1000 SX|Tandy 1000 SX]] CPUIn normal (high speed) mode. The 1000 SX also has a slower 4.77 MHz mode ({{frac|4|3}}''f'' ) for IBM PCjr compatibility. (and many other IBM PC-XT clones)
|-
| [[TurboGrafx-16]] CPU
|-
| [[Yamaha TX81Z]] synthesizer CPU
|-
| [[Amateur radio]] Tx/Rx crystal for 40m band
|-
| [[Sega Genesis|Genesis]] CPU
| 7.6705 MHz
| {{sfrac|15|7}}''f''
|-
| Intermediate frequency of FM radio superheterodyne circuits
| 10.7386 MHz
| 3''f''
|-
| [[High Precision Event Timer]] (typical)
| 14.3181 MHz
| 4''f''
|}
{{Table alignment}}
{| class="wikitable sortable col3center"
|+ Non-television uses of PAL colour burst frequency
(generally only in the PAL version of each device):
''f'' = 283.75 × 15625 Hz + 25 Hz = {{val|4.43361875|u=MHz}}
! Component
! Frequency
! Ratio
|-
| [[Commodore 64]] CPU
| rowspan="2" | 0.9852 MHz
| rowspan="2" | {{sfrac|2|9}}''f''
|-
| [[Commodore 128]] CPU (SLOW & [[C64]] compatible modes)
|-
| [[Atari 2600]] CPU
| 1.182298 MHz
| {{sfrac|4|15}}''f''
|-
| [[VIC-20]] CPU
| 1.1084 MHz
| {{sfrac|1|4}}''f''
|-
| [[Nintendo Entertainment System]] CPU[http://wiki.nesdev.com/w/index.php/Clock_rate NES DEV wiki: Clock Rate]
| 1.662607 MHz
| {{sfrac|3|8}}''f''
|-
| [[Atari 8-bit computers]] CPU
| rowspan="2" | 1.7734475 MHz
| rowspan="2" | {{sfrac|2|5}}''f''
|-
| [[Dendy]] ([[famiclone]]) CPU
|-
| [[Commodore 128]] CPU (FAST & CP/M modes)
| 1.9704 MHz
| {{sfrac|4|9}}''f''
|-
| rowspan="2" | [[Super Nintendo Entertainment System]] CPU
| 2.6601712 MHz
| {{sfrac|3|5}}''f''
|-
| 3.546895 MHz
| style="text-align:center" | {{sfrac|4|5}}''f''
|-
| Commodore [[Amiga]] CPU
| 7.09379 MHz
| {{sfrac|8|5}}''f''
|}
== See also ==
* [[Camera control unit]]
* [[Color framing]]
* [[Color killer]]
* [[Glossary of video terms]]
* [[Sync pulse]]
== References ==
{{reflist}}
== Notes ==
{{notelist}}
{{Analogue TV transmitter topics}}
[[Category:Video signal]]
[[Category:Television terminology]]
{{For|the instant camera range|Kodak Colorburst}}
{{Refimprove|date=September 2014}}
[[File:Commodore 64 PAL horizontal sync and colourburst.jpg|200px|right|thumb|Horizontal sync and color burst of the composite output of a [[Commodore 64]] computer]]
The '''color burst''' is one part of the composite sync used in analog television signals. It consists of a "packet" of the sine wave chroma subcarrier and is used as a reference to decode color information in the video. By synchronizing an [[Electronic oscillator|oscillator]] with the color burst at the [[Analog television#Structure of a video signal|back porch]] (beginning) of each [[scan line]], a television receiver is able to restore the suppressed carrier of the [[chrominance]] (color) signals, and in turn decode the color information.
== Explanation ==
In [[NTSC]], the color burst frequency is exactly 315/88 = 3.579{{overline|54}}{{efn|name=repeating decimal|[[Repeating decimal#Notation|Repeating decimal notation]]}} [[MHz]] with a phase of 180°. [[PAL]] uses a frequency of exactly 4.43361875 MHz, with its phase alternating between 135° and 225° from line to line. Since the color burst signal has a known amplitude, it is sometimes used as a reference level when compensating for amplitude variations in the overall signal.
[[SECAM]] is unique in not having a color burst signal, since the chrominance signals are encoded using [[Frequency modulation|FM]] rather than [[QAM]], thus the signal phase is immaterial and no reference point is needed.
== Rationale for NTSC Color burst frequency ==
{{Details|NTSC#Color encoding}}
The original black and white NTSC television standard specified a frame rate of 30 Hz and 525 lines per frame, or 15750 lines per second. The audio was frequency modulated 4.5 MHz above the video signal. Because this was black and white, the video consisted only of luminance (brightness) information. Although all of the space in between was occupied, the line-based nature of the video information meant that the luminance data was not spread uniformly across the [[frequency domain]]; it was concentrated at multiples of the line rate. Plotting the video signal on a [[spectrogram]] gave a signature that looked like the teeth of a comb or a gear, rather than smooth and uniform.
[[RCA Corporation|RCA]] discovered{{cite journal |last=Brown and Luck|date=June 1953 |title=Principles and development of color television systems |url=http://www.americanradiohistory.com/ARCHIVE-RCA/RCA-Review/RCA-Review-1953-June.pdf |journal=RCA Review |volume=XIV |pages=155–156}} that if the [[chrominance]] (color) information, which had a similar spectrum, was modulated on a carrier that was a [[half-integer]] multiple of the line rate, its signal peaks would fit neatly between the peaks of the luminance data and interference was minimized. It was not eliminated, but what remained was not readily apparent to human eyes. (Modern televisions attempt to reduce this interference further using a [[comb filter]].)
To provide sufficient bandwidth for the chrominance signal, yet interfere only with the highest-frequency (and thus least perceptible) portions of the luminance signal, a chrominance subcarrier near 3.6 MHz was desirable. 227.5 = 455/2 times the line rate was close to the right number, and 455's small factors (5 × 7 × 13) make a divider easy to construct.
However, additional interference could come from the [[audio signal]]. To minimize interference there, it was similarly desirable to make the distance between the chrominance [[carrier frequency]] and the audio carrier frequency a half-integer multiple of the line rate. The sum of these two half-integers implies that the distance between the frequency of the luminance carrier and audio carrier must be an integer multiple of the line rate. However, the original NTSC standard, with a 4.5 MHz carrier spacing and a 15750 Hz line rate, did not meet this requirement: the audio was 285.714 times the line rate.
While existing black and white receivers could not decode a signal with a different audio carrier frequency, they could easily use the copious timing information in the video signal to decode a slightly slower line rate. Thus, the new color television standard reduced the line rate by a factor of 1.001 to 1/286 of the 4.5 MHz audio subcarrier frequency, or about 15734.2657 Hz. This reduced the frame rate to 30/1.001 ≈ 29.9700 Hz, and placed the color subcarrier at 227.5/286 = 455/572 = 35/44 of the 4.5 MHz audio subcarrier.{{cite web |url=https://www.antiqueradio.org/art/NTSC%20Signal%20Specifications.pdf |title=NTSC Signal Specifications |date=23 May 2018 |website=Antique Radio.org}}
== Crystals ==
An NTSC or PAL television's color decoder contains a color burst [[crystal oscillator]].
Because so many analog color TVs were produced from the 1960s to the early 2000s, [[economies of scale]] drove down the cost of color burst crystals, so they were often used in various other applications, such as [[Electronic oscillator|oscillators]] for [[microprocessor]]s or for [[amateur radio]]: 3.5795 MHz has since become a common [[QRP operation|QRP]] calling frequency in the [[80-meter band]], and its [[frequency multiplier|doubled]] frequency of 7.159 MHz is a common calling frequency in the [[40-meter band]]. Tripling this frequency is also how [[FM radio]] circuits came to use a nominally 10.7 MHz [[intermediate frequency]] in [[Superheterodyne transmitter|superheterodyne]] conversion.
{{Table alignment}}
{| class="wikitable sortable col3center"
|+ Non-television uses of NTSC color burst frequency
(generally only in the NTSC version of each device):
''f'' = 315 MHz/88 = 3.579{{overline|54}}{{efn|name=repeating decimal}} MHz
! Component
! Frequency
! Ratio
|-
| [[Intellivision]] CPU
| rowspan="2" | 0.8949 MHz
| rowspan="2" | {{sfrac|4}}''f''
|-
| [[TRS-80 Color Computer]] CPU (normal speed)
|-
| [[Apple II]] CPU (short cycles only, one in 65 cycles is longer)
| rowspan="4" | 1.0227 MHz
| rowspan="4" | {{sfrac|2|7}}''f''
|-
| [[VIC-20]] CPU
|-
| [[Commodore 64]] CPU
|-
| [[Commodore 128]] CPU (SLOW & [[C64]] compatible modes)
|-
| [[Atari 2600]] CPU Atari 2600 Specifications http://problemkaputt.de/2k6specs.htm
| rowspan="2" | 1.1932 MHz
| rowspan="2" | {{sfrac|3}}''f''
|-
| [[Intel 8253]] interval timer in IBM PC (remains in use {{As of|2008|alt=today}})
|-
| [[Fairchild Video Entertainment System]] CPU
| rowspan="6" | 1.7898 MHz
| rowspan="6" | {{sfrac|2}}''f''
|-
| [[Odyssey 2]] CPU
|-
| [[Atari 8-bit computers]]{{cite book |title=Altirra Hardware Reference Manual |chapter=3.3 Cycle Timings |page=43 |first=Avery |last=Lee |date=2024-09-21 |access-date=2024-11-27 |url=http://www.virtualdub.org/downloads/Altirra%20Hardware%20Reference%20Manual.pdf#page=43}} and [[Atari 7800]] CPU
|-
| [[Plus/4]] CPU
|-
| [[Nintendo Entertainment System]] CPU
|-
| [[TRS-80 Color Computer#Color Computer 3 (1986%E2%80%931991)|TRS-80 Color Computer 3]] CPU (fast mode)
|-
| [[Commodore 128]] CPU (FAST & CP/M modes)
| 2.0454 MHz
| {{sfrac|4|7}}''f''
|-
| rowspan="2" | [[Super NES]] CPU
| 2.6847 MHz
| {{sfrac|3|4}}''f''
|-
| rowspan="7" | 3.5795 MHz
| style="text-align:center" | ''f''
|-
| [[Master System]] CPU
| rowspan="6" style="text-align:center" | ''f''
|-
| [[MSX]] CPU
|-
| [[Amateur radio]] Tx/Rx crystal for 80m band
|-
| [[ColecoVision]] CPU
|-
| [[Yamaha OPL|Yamaha OPL and OPL2]] FM synthesis sound chips
|-
| [[ACPI]] power management timer
|-
| [[IBM Personal Computer]] 5150 CPU
| 4.7727 MHz
| {{sfrac|4|3}}''f''
|-
| [[Amiga]] CPU
| rowspan="5" | 7.1591 MHz
| rowspan="5" | 2''f''
|-
| [[Tandy 1000#Tandy 1000 TX and Tandy 1000 SX|Tandy 1000 SX]] CPUIn normal (high speed) mode. The 1000 SX also has a slower 4.77 MHz mode ({{frac|4|3}}''f'' ) for IBM PCjr compatibility. (and many other IBM PC-XT clones)
|-
| [[TurboGrafx-16]] CPU
|-
| [[Yamaha TX81Z]] synthesizer CPU
|-
| [[Amateur radio]] Tx/Rx crystal for 40m band
|-
| [[Sega Genesis|Genesis]] CPU
| 7.6705 MHz
| {{sfrac|15|7}}''f''
|-
| Intermediate frequency of FM radio superheterodyne circuits
| 10.7386 MHz
| 3''f''
|-
| [[High Precision Event Timer]] (typical)
| 14.3181 MHz
| 4''f''
|}
{{Table alignment}}
{| class="wikitable sortable col3center"
|+ Non-television uses of PAL colour burst frequency
(generally only in the PAL version of each device):
''f'' = 283.75 × 15625 Hz + 25 Hz = {{val|4.43361875|u=MHz}}
! Component
! Frequency
! Ratio
|-
| [[Commodore 64]] CPU
| rowspan="2" | 0.9852 MHz
| rowspan="2" | {{sfrac|2|9}}''f''
|-
| [[Commodore 128]] CPU (SLOW & [[C64]] compatible modes)
|-
| [[Atari 2600]] CPU
| 1.182298 MHz
| {{sfrac|4|15}}''f''
|-
| [[VIC-20]] CPU
| 1.1084 MHz
| {{sfrac|1|4}}''f''
|-
| [[Nintendo Entertainment System]] CPU[http://wiki.nesdev.com/w/index.php/Clock_rate NES DEV wiki: Clock Rate]
| 1.662607 MHz
| {{sfrac|3|8}}''f''
|-
| [[Atari 8-bit computers]] CPU
| rowspan="2" | 1.7734475 MHz
| rowspan="2" | {{sfrac|2|5}}''f''
|-
| [[Dendy]] ([[famiclone]]) CPU
|-
| [[Commodore 128]] CPU (FAST & CP/M modes)
| 1.9704 MHz
| {{sfrac|4|9}}''f''
|-
| rowspan="2" | [[Super Nintendo Entertainment System]] CPU
| 2.6601712 MHz
| {{sfrac|3|5}}''f''
|-
| 3.546895 MHz
| style="text-align:center" | {{sfrac|4|5}}''f''
|-
| Commodore [[Amiga]] CPU
| 7.09379 MHz
| {{sfrac|8|5}}''f''
|}
== See also ==
* [[Camera control unit]]
* [[Color framing]]
* [[Color killer]]
* [[Glossary of video terms]]
* [[Sync pulse]]
== References ==
{{reflist}}
== Notes ==
{{notelist}}
{{Analogue TV transmitter topics}}
[[Category:Video signal]]
[[Category:Television terminology]]
