On Monday 19 November 2007 20:28, Ernest - (AfriNIC) wrote: > yes, hdtv requires about 37MHz while PAL (what we use in > UG) requires about 4MHz (but i'm sure you meant data > rates - in which case, HDTV needs approx 1GB/s)
Not quite. Depending on several factors (resolution, interlacing or progressive, number of channels being broadcast, encoding technique, modulation technique, e.t.c.), the general bit-rate for HDTV signals is between 19.3Mbps and 38.8Mbps; 19.3Mbps (well, 18Mbps for practical purposes) being the maximum for terrestrial broadcasts, while cable service providers can choose to push between 27.7Mbps to 38.8Mbps depending on the modulation technique. On a 6MHz cable slot using a 256 QAM modulation, cable service providers can transmit up to two 18Mbps channels. OTA (over-the-air) broadcasts could utilize up to 32Mbps as error-correction is included in the signal. Also, different service providers use different channels, e.g., cable service providers will use 6MHz, while DirecTv, for instance, would use 24MHz to 36MHz). Both would use different modulation techniques, as well. Some satellite service providers can offer as much as 27Mbps on a transponder. The thing to remember is that the more channels HDTV service providers cram into the package, the lower the bit-rate for each individual channel, and hence, the poorer the quality all-around. With HDTV, less is more... Cheers, Mark.
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