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sofakng3

join:2007-08-25
Kingston, PA

[HD] Is OTA higher quality than Comcast cable? (re: QAM channels

I've been looking at the setup in my area (Northeastern Pennsylvania) and my OTA channels have one network per channel. (i.e. frequency)

Example:
WNEP (ABC) HD = 50-3
WNEP2 SD = 50-4

WBRE (NBC) HD = 11

However, Comcast combines all three into one QAM256 channel. Therefore, if both HD channels were broadcasting at 19 Mbps, the QAM channel would need to be compressed to support all three feeds.

Therefore... is OTA the better choice for local channels even if you are paying for Comcast cable?

(NOTE: When I'm talking about channels above, I'm talking about ATSC frequencies and not virtual channel numbers)



telcodad
Premium
join:2011-09-16
Lincroft, NJ
kudos:15

Re: [HD] Is OTA higher quality than Comcast cable? (re: QAM chan

As your example shows, many OTA stations have a number of sub-channels in their transmission besides their main, HD one.

That means they all must share that 19 Mbps MPEG-2 ATSC video stream's bandwidth.

Given that, though, in most cases an OTA HD channel will exhibit higher PQ than that of the same channel on cable.

As was discussed in a previous thread of yours »Does Comcast use 3 or 4 channels per QAM? (MPEG2 bitrates) Comcast usually multiplexes 3 HD channels into one 38 Mbps 256-QAM carrier, so that the PQ of each channel is noticeably reduced.


sofakng3

join:2007-08-25
Kingston, PA

OK - Thanks. I was just making sure that I understood everything correctly.

It looks like 2x ATSC HD channels will fit perfect into one QAM256 channel (2 x 19 Mbps = 38 Mbps), but adding anything else, even an SD channel, will cause the HD streams to be recompressed. (** assuming they are both broadcasting at the full 19 Mbps which seems incredibly rare).



MN Comcast

@tough.us

I don't think Comcast or many cable providers re-compress the local channels... they send them straight through in the same quality. I know in the Minneapolis area they don't do it. It sucks because so many local affiliates don't broadcast HD at 19mbps due to sub channels. I think CBS is the highest here at ~16, Fox is usually ~14

Cable channels are a different story, anything other then sports channels (NFLN, ESPN, MSNBCSN) seems to be 3 per QAM... about 13mbps per channel.


logger

join:2012-06-14
Carmel, NY

said by MN Comcast :

I don't think Comcast or many cable providers re-compress the local channels... they send them straight through in the same quality.

I agree. The effect bit per second data rate supported by 6MHz channel depends on the modulation used. With 8vsb, used for over-the-air transmission, it is 19Mbps. With QAM, used for cable transmission, it is 38Mbps. (from »hd.engadget.com/2009/05/08/hd-10···d-8-vsb/).

Compared to a cable digital modulation technique, an over-the-air digital modulation technique uses additional error correction bits to recover from ways in which over-the-air signals degrade.

andyross
Premium,MVM
join:2003-05-04
Schaumburg, IL
reply to MN Comcast

said by MN Comcast :

Cable channels are a different story, anything other then sports channels (NFLN, ESPN, MSNBCSN) seems to be 3 per QAM... about 13mbps per channel.

It should be noted that the bandwidth is not fixed. The 3:1 channels are typically dynamic and the bandwidth will vary, with the total kept below 38Mbit.


camper
Premium
join:2010-03-21
Bethel, CT
kudos:1
Reviews:
·Comcast
reply to sofakng3

said by sofakng3:

...It looks like 2x ATSC HD channels will fit perfect into one QAM256 channel (2 x 19 Mbps = 38 Mbps), but adding anything else, even an SD channel, will cause the HD streams to be recompressed. (** assuming they are both broadcasting at the full 19 Mbps which seems incredibly rare).

You can check the broadcast bitrates here.

Just click on the link for Technical Data and Screencaps, and then scroll down a bit until you see the table of data.