5 ms·

Explains the PAL region epithet for NTSC - Never Twice the Same Color

anyfoo 4y ago
Yep, that's the reason! The ingenious idea of using quantum amplitude modulation unfortunately also meant that slight phase shifts--which happen easily in broadcast TV--appear as color errors. PAL fixed it by flipping the phase around every line. By subtracting the current line from the previous line, the phase error would cancel out (but is also more expensive since you need to remember the last line, in a delay line or memory[1]). So, always the same color. (But not ATSC, that's something else entirely...) [1] Well, there wer supposedly "PAL simple" receivers in the very beginning, where no processing of the phase flip was done and your eye was supposed to average the difference out. Probably looked terrible unless you were sitting really far away...
- namibj 4y ago
  Old PAL typically used a quartz prism that served as a folded bulk acoustic wave delay line, using an ultrasonic transducer and exciting the low syndic range of a composite signal to get by with cheap transducer electronics.
  - anyfoo 4y ago
    Intrigued now, where can I find more about that?
    - nyanpasu64 4y ago
      https://en.wikipedia.org/wiki/Analog_delay_line https://en.wikipedia.org/wiki/Analog_delay_line, https://commons.wikimedia.org/wiki/File:Us_delay_line.jpg https://commons.wikimedia.org/wiki/File:Us_delay_line.jpg
  - greesil 4y ago
    Good god, the things people used to do because transistors weren't available, or too expensive.
    - zokier 4y ago
      There is not really good way of accomplishing with transistors what delay lines are used for in PAL, unless you go full digital.
      - anyfoo 4y ago
        I guess you could take a massive amount of them, and some capacitors, and use them for sample and hold. But you already covered insanity like that by saying that there is no good way...
        frabert 4y ago
        That's called a Bucket-brigade device btw
        anyfoo 4y ago
        Wow, indeed, that actually exists just like that…
- deaddodo 4y ago
  This is one of this things I always found funny about PAL vs NTSC arguments. There simply wasn’t a better option, at the time. Both options were engineered with limited resources to best fit their respective needs. NTSC had a better refresh rate and easier hardware integration, plus 70+ years of backwards/forwards compatibility (a 1941 NTSC B+W television set could be used to watch the series finale of Friends in 2004 using a bog standard antenna for over the air signals); PAL had almost 30 years of experience and fixed some of the major issues with NTSC (primarily the Phase signaling) and had increased resolution at the cost of refresh rates. Both were pushing analog transmission bandwidth to the limits and did admirably until digital options were available and became the norm.
- MayeulC 4y ago
  s/quantum/quadratic/ (you got me confused for a second)
  - anyfoo 4y ago
    Ugh yeah. That comment, unlike my original one, is full of typos. I typed it out quickly on my phone, and can’t edit anymore.
msla 4y ago
That was a problem early on, maybe, but probably by the 1980s and certainly by the 1990s, it was a dead issue in terms of consumer TVs that weren't antiques or damaged somehow.
iso1631 4y ago
I believe when they fixed it with digital, the standard was renamed to "Always Twice the Same Colour"
- LocalH 4y ago
  I find it hilarious (in a mildly sad way) that NTSC (or any other analog system) is a far better system for final delivery when conditions aren't effectively perfect. Guarantee you that a digital broadcast will break down far before any analog broadcast will. If only digital could be used for 99% of distribution, with OTA still being at least some sort of hybrid system for better resilience. Digital broadcasting has very low resilience to interference. Speaking from a US perspective here, where we got saddled with 8VSB (from my understanding, COFDM is much more resilient).
  - iso1631 4y ago
    That's not right. Digital transmission systems will cope with the errors and regenerate a perfect signal upto a point called the digital cliff. With that amount of noise in an analog signal will be a very snowy, staticy, picture. In an analog signal, a bright picture will be 700mV, a less bright picture will be 500mV, a dark one at 200mV and a very dark one at 50mV. Imagine that you get a 300mV error, that loses a lot of data - the dark one will be sort of bright, or vice versa, or the sort-of bright will be really-bright, etc. Now lets say you have a 1 represented by an amplitude of 700mV, and a 0 represented by 50mV. A 300mV error wlll have it at 400mV and 350mV. Your system will go "hey this is 350mV, it's a zero", and reclock it to 50mV, and vice versa. The recovered signal will be identical upto the point that the errors flip the bits - the digital cliff. (In reality of course the signal isn't just high/low but uses various techniques to encode the ones and zeros to prevent DC voltages accruing - Manchester Encoding for example. Push an analog video signal down a cable and it will degrade the longer the cable is. The same will happen in the digital domain -- you can see this on a waveform monitor by looking at the digital eye, but as long as the eye is open enough the signal can be retrieved to it's original state. With an analog signal, the signal is lost, and can't be retrieved.
    - 4y ago

Yep, that's the reason! The ingenious idea of using quantum amplitude modulation unfortunately also meant that slight phase shifts--which happen easily in broadcast TV--appear as color errors. PAL fixed it by flipping the phase around every line. By subtracting the current line from the previous line, the phase error would cancel out (but is also more expensive since you need to remember the last line, in a delay line or memory[1]). So, always the same color. (But not ATSC, that's something else entirely...) [1] Well, there wer supposedly "PAL simple" receivers in the very beginning, where no processing of the phase flip was done and your eye was supposed to average the difference out. Probably looked terrible unless you were sitting really far away...

namibj 4y ago
Old PAL typically used a quartz prism that served as a folded bulk acoustic wave delay line, using an ultrasonic transducer and exciting the low syndic range of a composite signal to get by with cheap transducer electronics.
- anyfoo 4y ago
  Intrigued now, where can I find more about that?
  - nyanpasu64 4y ago
    https://en.wikipedia.org/wiki/Analog_delay_line https://en.wikipedia.org/wiki/Analog_delay_line, https://commons.wikimedia.org/wiki/File:Us_delay_line.jpg https://commons.wikimedia.org/wiki/File:Us_delay_line.jpg
- greesil 4y ago
  Good god, the things people used to do because transistors weren't available, or too expensive.
  - zokier 4y ago
    There is not really good way of accomplishing with transistors what delay lines are used for in PAL, unless you go full digital.
    - anyfoo 4y ago
      I guess you could take a massive amount of them, and some capacitors, and use them for sample and hold. But you already covered insanity like that by saying that there is no good way...
      - frabert 4y ago
        That's called a Bucket-brigade device btw
        anyfoo 4y ago
        Wow, indeed, that actually exists just like that…
deaddodo 4y ago
This is one of this things I always found funny about PAL vs NTSC arguments. There simply wasn’t a better option, at the time. Both options were engineered with limited resources to best fit their respective needs. NTSC had a better refresh rate and easier hardware integration, plus 70+ years of backwards/forwards compatibility (a 1941 NTSC B+W television set could be used to watch the series finale of Friends in 2004 using a bog standard antenna for over the air signals); PAL had almost 30 years of experience and fixed some of the major issues with NTSC (primarily the Phase signaling) and had increased resolution at the cost of refresh rates. Both were pushing analog transmission bandwidth to the limits and did admirably until digital options were available and became the norm.
MayeulC 4y ago
s/quantum/quadratic/ (you got me confused for a second)
- anyfoo 4y ago
  Ugh yeah. That comment, unlike my original one, is full of typos. I typed it out quickly on my phone, and can’t edit anymore.

msla 4y ago

That was a problem early on, maybe, but probably by the 1980s and certainly by the 1990s, it was a dead issue in terms of consumer TVs that weren't antiques or damaged somehow.

iso1631 4y ago

I believe when they fixed it with digital, the standard was renamed to "Always Twice the Same Colour"

LocalH 4y ago
I find it hilarious (in a mildly sad way) that NTSC (or any other analog system) is a far better system for final delivery when conditions aren't effectively perfect. Guarantee you that a digital broadcast will break down far before any analog broadcast will. If only digital could be used for 99% of distribution, with OTA still being at least some sort of hybrid system for better resilience. Digital broadcasting has very low resilience to interference. Speaking from a US perspective here, where we got saddled with 8VSB (from my understanding, COFDM is much more resilient).
- iso1631 4y ago
  That's not right. Digital transmission systems will cope with the errors and regenerate a perfect signal upto a point called the digital cliff. With that amount of noise in an analog signal will be a very snowy, staticy, picture. In an analog signal, a bright picture will be 700mV, a less bright picture will be 500mV, a dark one at 200mV and a very dark one at 50mV. Imagine that you get a 300mV error, that loses a lot of data - the dark one will be sort of bright, or vice versa, or the sort-of bright will be really-bright, etc. Now lets say you have a 1 represented by an amplitude of 700mV, and a 0 represented by 50mV. A 300mV error wlll have it at 400mV and 350mV. Your system will go "hey this is 350mV, it's a zero", and reclock it to 50mV, and vice versa. The recovered signal will be identical upto the point that the errors flip the bits - the digital cliff. (In reality of course the signal isn't just high/low but uses various techniques to encode the ones and zeros to prevent DC voltages accruing - Manchester Encoding for example. Push an analog video signal down a cable and it will degrade the longer the cable is. The same will happen in the digital domain -- you can see this on a waveform monitor by looking at the digital eye, but as long as the eye is open enough the signal can be retrieved to it's original state. With an analog signal, the signal is lost, and can't be retrieved.
  - 4y ago