Not just a digital TV aerial...

Steve Thackery wrote:
Jim Lesurf wrote:

But the main factor is
probably that the HD mux(s) use 256 QAM I think, which means you need
higher carrier/noise to decode with the same raw error rate than the
SD muxes. Not done the math, though.

That is my understanding - 256 QAM makes the signal inherently more
fragile. Happy to be corrected, though.

.....but the 32k carriers should restore the robustness ? :-)



--
Mark
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In message , Steve Thackery
writes
Jim Lesurf wrote:

But the main factor is
probably that the HD mux(s) use 256 QAM I think, which means you need
higher carrier/noise to decode with the same raw error rate than the
SD muxes. Not done the math, though.

That is my understanding - 256 QAM makes the signal inherently more
fragile. Happy to be corrected, though.

Doesn't the change from 64 to 256 QAM mean that the SNR/MER has to be
6dB better?
--
Ian

Steve Thackery wrote:
Mark Carver wrote:

You mean a DVB-T2 transmission is more fragile than a T1 one ?

Well, I think so. I don't claim to understand the technical details.
Rather, I can claim considerable experience as I lived in a marginal
reception area where break-up was problematical.
That isn't considerable experience.

HD channels were
affected far more than SD channels. I guess it's a pretty safe bet
that this is caused by T2 being more fragile than T1.
How about the possibility that the signal/noise ratio on the HD mux was
worse?

Bill

Mark Carver wrote:

....but the 32k carriers should restore the robustness ? :-)

Is that right, then? I don't know.....

--
SteveT

Steve Thackery wrote:
Mark Carver wrote:

....but the 32k carriers should restore the robustness ? :-)

Is that right, then? I don't know.....

Nor do I

http://www.dvb.org/technology/fact_s..._Factsheet.pdf

This from the DVB committee website, says that T2 can offer more
payload *OR* significantly more robust reception.

The notes attached to the table on the pdf sort of answer the question (I think !)


--
Mark
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Steve Thackery wrote:

I can claim considerable experience as I lived in a marginal
reception area where break-up was problematical. HD channels were
affected far more than SD channels. I guess it's a pretty safe bet
that this is caused by T2 being more fragile than T1.

Is that correct, from a technical point of view?

It could be that the frequency of the HD mux from your chosen
transmitter was out of group for your aerial, but all the SD ones were
within group.

Ignoring the DVB-T1/T2 transmission differences, the HD codec has a
higher compression, so if there are sufficient errors to overwhelm the
error correction, the same number of bytes of corruption will tend to
have a larger corrupting effect on the decompressed picture.

Andy Burns wrote:
Steve Thackery wrote:

I can claim considerable experience as I lived in a marginal
reception area where break-up was problematical. HD channels were
affected far more than SD channels. I guess it's a pretty safe bet
that this is caused by T2 being more fragile than T1.

Is that correct, from a technical point of view?

It could be that the frequency of the HD mux from your chosen
transmitter was out of group for your aerial, but all the SD ones were
within group.

Ignoring the DVB-T1/T2 transmission differences, the HD codec has a
higher compression, so if there are sufficient errors to overwhelm the
error correction, the same number of bytes of corruption will tend to
have a larger corrupting effect on the decompressed picture.

If a single HD channel occupied the mux, and all of its capacity,
that might be true, but isn't the data from each service in effect
interleaved to create the transport stream, and therefore the risk
of total loss of any service reduced ?

--
Mark
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On 21/04/2013 20:35, Mark Carver wrote:
This from the DVB committee website, says that T2 can offer more
payload *OR* significantly more robust reception.

Past experience of DAB and the ever shrinking bit budget makes me
suspect they'll have gone for payload, not robustness.

Andy

Jim Lesurf wrote:
In article , David.WE.Roberts
wrote:
.....but an HD Digital TV Aerial.

However this did make me wonder if you needed a better quality signal to
be able to receive HD programmes. Assuming a higher bit rate for the
content, does this lose data more easily in marginal signal areas
compared to an SD broadcast?

The higher bitrate does make a 'bigger target'. But the main factor is
probably that the HD mux(s) use 256 QAM I think, which means you need
higher carrier/noise to decode with the same raw error rate than the SD
muxes. Not done the math, though.

I don't know about that aspect, but another thing to consider is that HD
uses H264 and it could be that current mpeg2 decoders with years of
experience are better at error concelement/recovery that newer h264
ones. The coding of h264 also uses fewer reference frames than mpeg2 so
I guess there's the potential for data loss to affect more pictures.

Bill Wright wrote:

That isn't considerable experience.

OK, probably not.

How about the possibility that the signal/noise ratio on the HD mux
was worse?

That's probably true. What is your experience: have you found HD
channels to be more "fragile"?

--
SteveT