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Snowy analog with intelligible sound translates to about 40dB signal to noise ratio. That's a SNR where digital will deliver crystal clear image. When digital b

by yholio 5y ago

Snowy analog with intelligible sound translates to about 40dB signal to noise ratio. That's a SNR where digital will deliver crystal clear image. When digital becomes glitchy, you will absolutely be unable to watch analogue, you will have trouble maintaining vertical and horizontal sync and the sound will be drowned in noise.

blendergeek 5y ago
So that may be true, in theory. In reality, the switch from Analog to Digital means that while people in Urban areas have more clearer channels, people in rural areas (who could watch snow covered analog TV) now have fewer if any channels. Even if a mathematical calculation says that my TV should work great, I still have nothing if I can't pick up any channels.
- uxp100 5y ago
  Even in urban areas we lost broadcasters in the transition to digital. It is just worse in a lot of ways. I don't care that my morning weather report is clearer in picture, if it stutters seemingly randomly. It's not as far as unintelligible, just fantastically irritating.
dkarl 5y ago
There must be some other factor at work, then, because I had the same experience when I didn't have cable around 2010. For a few big sports events I tried to get broadcasts, and analog was watchable (by analog standards) when digital was unwatchable because of frequent glitching. Buying a fancy antenna did not help. Maybe television stations did not care enough about broadcast anymore to invest in digital broadcasting capability that matched the power of their old analog broadcasts.
- yholio 5y ago
  There are many factors that come into this. The bandwidth of a single analog channel can accommodate 4 or more digital channels. If the transmitter is not upgraded, its power will now be spread to multiple channels. Another is simply self-selection bias. When a rapid technical transition takes place, the average reception might improve significantly, but you can't guarantee it for everyone. A slight frequency change, a reflection pattern can drastically alter the signal intensity in a certain spot. But you will only hear from people who happened to have good analog and lost it, those with bad analog had already moved to cable and are unaware that good terrestrial digital has become available. My experience with Freeview in the greater London area was very positive, with a very simple antenna I was able to get around 100 channels, the vast majority in perfect quality.
  - salamandersauce 5y ago
    Does ATSC/NTSC work the same way as DVB-T/PAL with regards to signal quality at the same DB?
    - yholio 5y ago
      They are built upon the same basic principles - QAM modulation, error correcting codes and MPEG/HEVC codecs, so there should be no significant difference. The newest ATSC3.0 standard has a somewhat richer toolbox allowing the optional use of 1024 or 4096QAM vs 256QAM for DVB, more advanced LDPC error correcting codes, LDM multiplexing and MIMO. The industry seems to believe the added complexity is not worth the marginal benefits. The fundamental difference between Europe (or at least UK) and US seems to be the concern regulators had for improving over the air TV. So while in the UK, the move to digital was employed to broadly improve the offering and reception quality, in the US there was less concern and the stations found the death of analog a good opportunity to close down transmitters, recover spectrum and remove free programing.
  - blendergeek 5y ago
    The people I hear from had bad analog. But you can watch bad analog; your TV is just covered in snow. Bad digital is unwatchable.
- thedougd 5y ago
  Many, if not most stations switched broadcast frequency during the transition from analog to digital.
- handrous 5y ago
  I bet a bunch of them did some naïve calculation that said "because digital performs better, we can reduce broadcast power by X, for a savings of $Y, without loss of range", but real-world conditions meant this actually did reduce their broadcast range a little (though mostly in low-population areas they barely cared about anyway). This may have coincided with lower investment in broadcast, anyway. Replacing the transmitting equipment, don't care about providing as much range as the much older, analog equipment did, because the per-viewer value has dropped enough that it's not worth it to reach rural areas, so you cheap out on both equipment & broadcast strength.
- hulitu 5y ago
  It is. A so called digital signal is still an analog signal which must be processed. You only obtain the digital signal after you process it. The main issue here is that the digital signal is much more complex and due to this much sensible to noise. When it rains for example the analog signal will still be visible as long as the sync part can be decoded. For digital signal noise will be replaced by predicted frames. The issue is that a lot of providers have a very bad quality and they rely heavily on predicted frames. And when the key frames are not available (due to noise) good luck predicting the rest of the frames.
  - BenjiWiebe 5y ago
    Actually, thanks to error correcting codes, a digital signal can get right up against the Shannon limit. You can't improve on the Shannon limit.
  - yholio 5y ago
    The difference between sync level and black level in analog TV standards is about 15% of maximum transmitter power. This means that any noise added that is more than 7.5% of max power will confuse the TV to detect sync as black and black as sync. In practice, a 20dB SNR or less will be completely unwatchable. The Shannon limit for a 5Mhz channel with 20 dB SNR is 17 Mbit/s and latest DTV standards approach this, easily 10, maybe 15 Mbit. That's enough for a HD channel in perfect quality or many more in SD. So the problem is not with analog vs digital, that debate is long settled. It's the specific tradeoffs made when digital TV was deployed.
- rainbowzootsuit 5y ago
  One problem I've recently become aware of is that LTE and 5g cellular signals are overwhelming the digital TV signals by raising the noise floor in the amplifier stage even though they don't use the same frequencies.
- syntheticnature 5y ago
  One thing I don't see noted yet in the replies -- ATSC 1.0 (the current US standard) has awful difficulties with multipath signals (reflections off of buildings, terrain, etc.) ATSC 3.0 is supposed to fix this, but brings with it its own feature bloat.
jandrese 5y ago
The problem is that many stations migrated from well propagating VHF to UHF with the digital migration. The higher frequency signal experiences more fade due to atmospheric conditions and ground clutter. They also jam multiple channels into the same bandwidth the single old channel used to occupy, further reducing EIRP per channel.
- fomine3 5y ago
  VHF -> UHF transition is same here in Japan. After digital TV transition, empty VHF frequencies considered to worth for something like broadcast service for mobile device, so the service(NOTTV) started. But the service is failed due to not attracting (and partially because iPhone don't support it), so now not utilized again. How VHF frequencies utilized in other countries?

by yholio 5y ago

blendergeek 5y ago

So that may be true, in theory. In reality, the switch from Analog to Digital means that while people in Urban areas have more clearer channels, people in rural areas (who could watch snow covered analog TV) now have fewer if any channels. Even if a mathematical calculation says that my TV should work great, I still have nothing if I can't pick up any channels.

uxp100 5y ago
Even in urban areas we lost broadcasters in the transition to digital. It is just worse in a lot of ways. I don't care that my morning weather report is clearer in picture, if it stutters seemingly randomly. It's not as far as unintelligible, just fantastically irritating.

dkarl 5y ago

There must be some other factor at work, then, because I had the same experience when I didn't have cable around 2010. For a few big sports events I tried to get broadcasts, and analog was watchable (by analog standards) when digital was unwatchable because of frequent glitching. Buying a fancy antenna did not help. Maybe television stations did not care enough about broadcast anymore to invest in digital broadcasting capability that matched the power of their old analog broadcasts.

yholio 5y ago
There are many factors that come into this. The bandwidth of a single analog channel can accommodate 4 or more digital channels. If the transmitter is not upgraded, its power will now be spread to multiple channels. Another is simply self-selection bias. When a rapid technical transition takes place, the average reception might improve significantly, but you can't guarantee it for everyone. A slight frequency change, a reflection pattern can drastically alter the signal intensity in a certain spot. But you will only hear from people who happened to have good analog and lost it, those with bad analog had already moved to cable and are unaware that good terrestrial digital has become available. My experience with Freeview in the greater London area was very positive, with a very simple antenna I was able to get around 100 channels, the vast majority in perfect quality.
- salamandersauce 5y ago
  Does ATSC/NTSC work the same way as DVB-T/PAL with regards to signal quality at the same DB?
  - yholio 5y ago
    They are built upon the same basic principles - QAM modulation, error correcting codes and MPEG/HEVC codecs, so there should be no significant difference. The newest ATSC3.0 standard has a somewhat richer toolbox allowing the optional use of 1024 or 4096QAM vs 256QAM for DVB, more advanced LDPC error correcting codes, LDM multiplexing and MIMO. The industry seems to believe the added complexity is not worth the marginal benefits. The fundamental difference between Europe (or at least UK) and US seems to be the concern regulators had for improving over the air TV. So while in the UK, the move to digital was employed to broadly improve the offering and reception quality, in the US there was less concern and the stations found the death of analog a good opportunity to close down transmitters, recover spectrum and remove free programing.
- blendergeek 5y ago
  The people I hear from had bad analog. But you can watch bad analog; your TV is just covered in snow. Bad digital is unwatchable.
thedougd 5y ago
Many, if not most stations switched broadcast frequency during the transition from analog to digital.
handrous 5y ago
I bet a bunch of them did some naïve calculation that said "because digital performs better, we can reduce broadcast power by X, for a savings of $Y, without loss of range", but real-world conditions meant this actually did reduce their broadcast range a little (though mostly in low-population areas they barely cared about anyway). This may have coincided with lower investment in broadcast, anyway. Replacing the transmitting equipment, don't care about providing as much range as the much older, analog equipment did, because the per-viewer value has dropped enough that it's not worth it to reach rural areas, so you cheap out on both equipment & broadcast strength.
hulitu 5y ago
It is. A so called digital signal is still an analog signal which must be processed. You only obtain the digital signal after you process it. The main issue here is that the digital signal is much more complex and due to this much sensible to noise. When it rains for example the analog signal will still be visible as long as the sync part can be decoded. For digital signal noise will be replaced by predicted frames. The issue is that a lot of providers have a very bad quality and they rely heavily on predicted frames. And when the key frames are not available (due to noise) good luck predicting the rest of the frames.
- BenjiWiebe 5y ago
  Actually, thanks to error correcting codes, a digital signal can get right up against the Shannon limit. You can't improve on the Shannon limit.
- yholio 5y ago
  The difference between sync level and black level in analog TV standards is about 15% of maximum transmitter power. This means that any noise added that is more than 7.5% of max power will confuse the TV to detect sync as black and black as sync. In practice, a 20dB SNR or less will be completely unwatchable. The Shannon limit for a 5Mhz channel with 20 dB SNR is 17 Mbit/s and latest DTV standards approach this, easily 10, maybe 15 Mbit. That's enough for a HD channel in perfect quality or many more in SD. So the problem is not with analog vs digital, that debate is long settled. It's the specific tradeoffs made when digital TV was deployed.
rainbowzootsuit 5y ago
One problem I've recently become aware of is that LTE and 5g cellular signals are overwhelming the digital TV signals by raising the noise floor in the amplifier stage even though they don't use the same frequencies.
syntheticnature 5y ago
One thing I don't see noted yet in the replies -- ATSC 1.0 (the current US standard) has awful difficulties with multipath signals (reflections off of buildings, terrain, etc.) ATSC 3.0 is supposed to fix this, but brings with it its own feature bloat.

jandrese 5y ago

The problem is that many stations migrated from well propagating VHF to UHF with the digital migration. The higher frequency signal experiences more fade due to atmospheric conditions and ground clutter. They also jam multiple channels into the same bandwidth the single old channel used to occupy, further reducing EIRP per channel.

fomine3 5y ago
VHF -> UHF transition is same here in Japan. After digital TV transition, empty VHF frequencies considered to worth for something like broadcast service for mobile device, so the service(NOTTV) started. But the service is failed due to not attracting (and partially because iPhone don't support it), so now not utilized again. How VHF frequencies utilized in other countries?