Finally have digital TV
- Thread starter K.I.L.E.R
- Start date
Depends how you define image quality I suppose. The degradation when it happens come suddenly, instead of manifesting itself as a slow increase in, eg. noise. as it would with analogue. With digital you first seem to get skipping frames as signal strength drops, then when things get really bad it starts dropping blocks from the image. But the bits of the image that you do see look just as noise-free as when the signal strength is good. If that makes sense.K.I.L.E.R said:
I'm not totally convinced by terrestrial digital TV TBH. In the UK it seems to be being used as an excuse to crowbar as much crap telly with high compression ratios into the minimum bandwidth possible. The quality is nowhere near what is available on satellite, or even better on digital cable. This situation may improve after analogue switch-off frees up large chunks of the frequency spectrum, but apparently we have to wait for all the old people here to die before we can turn their analogue telly off.
The higher the reception level, the less the FEC system will work (Forward Error Correction), which is a DVB stream (if we are talking about DVB transmissions) error correction thanks to redundant bits. Actually DVB uses a two layered FEC, employing Viterbi on the top layer and Reed-Solomon on the bottom layer, plus Interleaving/Deinterleaving to correct burst errors.
The new DVB-S2 (only for satellite now, but I guess it'll later be employed by any DVB transmissions) standard uses a different FEC system, mainly based on low density parity check (LDPC) concatenated with the Bose Chaudhuri Hochquenghem code
The new DVB-S2 (only for satellite now, but I guess it'll later be employed by any DVB transmissions) standard uses a different FEC system, mainly based on low density parity check (LDPC) concatenated with the Bose Chaudhuri Hochquenghem code
Does it also have a "signal quality" value? It means roughly the error rate of the demodulator. Sometimes when the signal becomes too strong, it's clamped and can't be properly decoded. A proper implementation should have a feedback mechanism which adjusts the signal level according to the strength. But signal strength does not always correlates to signal quality.
It will -- in a way.K.I.L.E.R said:
DVB (which is what's in Europe and Australia) uses Reed-Solomon error correction, which means it can tolerate (i.e. correct) a certain number of errors in each packet of data before it has to ditch the packet. IIRC DVB uses 16 bytes of parity=> up to 8 byte errors can be corrected.
Obviously, a lower signal strength will increase the chances of errors and hence increase the probability of lost packets.
FWIW, I also just bought a DVB tuner for my PC. It's the size of a USB memory!
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