Looking into the audio/video specifications of the satellite channels using the latest generation DVB system, the state of the art h.264 video codec is employed instead of the old MPEG-2, but audio seems to be a different story. The outdated MP2 codec continues to be used. It is inefficient compared to HE-AAC as it is proved by the recent developements in DAB radio. MP2 dates back in the mid '80s. I can hear noticeable artifacts in many audio channels. As result of all these cosiderations I was wondering why satellite tv and radio operators don't take advantage of the latest MPEG audio technology like in video codecs?
The case of the adoption of Dolby AC3 in DVD and AVCHD instead of EAC3 or AAC I think is related to the widespread use of AC3 in the movie soudtracks.
I have read that scandinavian countries and Ireland use HE-AAC in terrestrial DVB-T, do they use AAC also for satellite tramissions?

Thank you

Enrico

As far as I know nobody is using it via satellite yet. But it's one of the defined audio codecs that is allowed with DVB (besides Layer 2, Dolby AC3 and DTS). IMHO it will just take some time until the Broadcasters recognise that they can save a lot bandwith with AAC and maybe squeeze another channel onto the transponder.

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As far as I know nobody is using it via satellite yet. But it's one of the defined audio codecs that is allowed with DVB (besides Layer 2, Dolby AC3 and DTS). IMHO it will just take some time until the Broadcasters recognise that they can save a lot bandwith with AAC and maybe squeeze another channel onto the transponder.
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I see, but I think that even hardware receivers on the market today do not feature AAC support, I can't find it in the tech specs at least, broadcaster would not use it if receivers didn't support it.

Well, all Vantage HD Receivers could decode AAC. The reason is that they have only one Firmware for the whole range of HD receivers and they also have some DVB-T / DVB-S2 Combo Receivers on sale. In the begining there was no support for AAC, it was added with a Firmware Update. As like 95% of all DVB-S2 Receivers use the same STi7100 chipsets as the Vantage Receivers (the big exception is Humax, which uses some Broadcom chipset), it should be absolutely no Problem to add AAC to most receivers via a Firmware upgrade if there is the need to it. DTS is also specified, but nearly no Receiver supports it, because it is only used at some swedish and norwegian channels (after SR did a listening test and it's consumers prefered 1.5Mbps DTS 5.1 Multichannel to 640kbps 5.1 AC3)

I'm working since 13 years in the satellite TV equipment bussiness. I've seen the first DVB-S transmissions and was amazed by the great picture quality. Therefore I spent lots of money to get the first DVB-S receiver, just to notice that year by year the picture quality gets worse because the broadcaster squeeze one channel after the other onto the transponders. I'm living in the region where DVB-T was tested first and because of my job I could test it and the picture quality was good. Therefore I was also one of the first who had a DVB-T receiver. But after the testing period was over they decided to put 4 TV channels into a DVB-T Bouquet instead of 3. Nowadays DVB-T is nearly unwatchable. The same is happening with DVB-S2: They squeeze 4 1080i HD channels onto one transponder or even use 720p because it uses a little less bandwidth.
Commercial digital video and audio is only great for the broadcasters, as it allows them to maximise the profit. The audio and video quality that is important for the viewer comes last to them.

vpa, I've seen the same decrease in quality, but...
...you're lucky! In the UK, we have a 24Mbps with 9 MPEG-2 SD channels.

The UK mux configurations are here:
http://www.lstar337.adsl24.co.uk/home.htm
which is the real link to here:
http://mymuxdata.tk/


Why don't DVB-S2 broadcasts use AAC audio? I guess many consumers are using the AC-3 output, so AAC would have to be transcoded to be sent to their amps. Plus broadcasters already have the AC-3 equipment. Most importantly, even if you switched the audio stream off(!) it would only save 384-448kbps which is nothing compared with the 15-20Mbps currently used for HD video.

I guess as HD video bitrates are pushed down, or where many multiple language soundtracks need to be broadcast, AAC will be a genuine benefit. For now, if it ain't broke, why fix it?

I think many European broadcasters are wondering what the benefit of MPEG-4 AVC (H.264) video is over MPEG-2, given that current encoders still need 16-20Mbps for really good results. They assume next generation encoders will make the choice of AVC worthwhile - it was a lot of money to spend on next generation STBs if they need to stick at 20Mbps into the future!

Cheers,
David.

Oh dear, 9 channels is realy a lot, even with the higher netto datarate of an UK DVB-T channel (like 64QAM, Guard Interval 1/8, FEC 1/4 = 24,88 Mbps). German DVB-T is meant for portable indoor usage and has therefore a lower netto datarate (like 16QAM, Guard Interval 1/4, FEC 2/3 = 13,27 Mbps)

Germany: 13,27 / 4 = 3,31 Mbps per channel
UK : 24,88 / 9 = 2,76 Mbps per channel

That's just terrible and has nothing to do with TV anymore. It might be only enjoyable for people who like moving MPEG blocking artefacts

It's a larger stat-mux pool, and of course it's hugely dependent on the encoder - so it's possible we have better quality than you even at a lower bitrate - but you're right, the quality is often poor.

People seem to accept it, but with the increase in large screen TVs with associated picture processing, scaling, sharpening etc, people are often watching little more than a sea of macroblocks!

Cheers,
David.

The problem with the use of digital compression is that it is far more flexible than the old analogue trasmissions. FM bandwidth is fixed, unless you replace all the existing receivers, Tv channel bandwidth was also fixed. With the advent of digital broadcasting technology quality is easily sacrified for profit. Even BBC HD source material is not mada of full 1080 * 1920 squre pixel pictures like in Blue Ray, but just a 1080 * 1440 rectangular pixel, meaning that the horizontal sesolution is lower, than compression ratio could be reduced as low as it is required like in DAB radio.
A quality standard should be imposed by the consumers who spend a lot of money on large flat screens.

If DTS is better than AC3, but requires a larger bitrate, is AAC or EAC3 good as DTS at a lower bitrate?

In my experience people not only don't notice MPEG blocking artifacts, LCD ghosting and deinterlacing jitter, they also are incapable of telling if the picture is even in the right aspect ratio.

Is there any commercial side to the codec choice for broadcast, for example does streaming AAC attract a time based royalty from MPEG-LA in a way that using AC-3 doesn't?

I agree, most of the people watch 4/3 aspect ratio tv in a 16/9 screen by deforming the picture in order to fill the entire frame, I find this an orrible habit. I'd rather keep the correct ascpet ratio with the two black side vertical bands.

True words. With digital it is unclear where is the threshold, at which the datastream can actually be called "video". At 3 Megabits it is technically still the supposedly superior "digital video".

A little while ago I raised similar concerns about audio broadcasting. It has often been expressed that DVB and DAB broadcasting is overly expensive. If this is true, then why the heck such a system was deployed in the first place?

In the case of DAB it was only deployed in about 3 countries and in the UK was a a combination of: miscalculation of time frames, staggering incompetence on the part of the regulator (ofcom) and management incompetence (which is still ongoing) at the BBC.

You can read about the whole sordid affair at http://www.digitalradiotech.co.uk/

It will, eventually, sort itself out as everywhere else is adopting DAB+ or a variant thereof. Therefore within a few years you'll only be able to buy receivers which support both DAB and DAB+ as it will not be economic to make DAB only modules. Once the majority of receivers supports DAB+ someone will want to launch DAB+ channels in the UK and ofcom are going to have a very hard job stopping them even if it take someone suing the government.

However this could take another decade or so to play out and events could be overtaken by internet streaming, Digital Radio Mondiale or even streaming over UTMS or LTE (although would be pretty bonkers), also nothing is going to change radically until whatever does end up replacing FM radio gets built into car dashboards.

They've changed the source requirements - it'll all be 1920x1080 before the end of the year. Whether they change the broadcasts remains to be seen.

They dropped the BBC HD bitrate from 20Mbps to 16Mbps earlier this year, but I think it's a bit unfair to compare that with BBC DAB radio (64-128kbps mp2, apart from Radio 3) which really is horrible.

Cheers,
David.

[quote name='2Bdecided' date='Sep 3 2008, 06:14' post='586183']
[/quote]They've changed the source requirements - it'll all be 1920x1080 before the end of the year. Whether they change the broadcasts remains to be seen.

They dropped the BBC HD bitrate from 20Mbps to 16Mbps earlier this year, but I think it's a bit unfair to compare that with BBC DAB radio (64-128kbps mp2, apart from Radio 3) which really is horrible.

Cheers,
David.
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I do understand nowadays it is unfair, but it could not be in a future scenario where more and more channels will be turned to HD requiring a lot of bandwidth.

Agreed - they are in an impossible situation on terrestrial, and I fear they'll cripple their HD offering on satellite so that it does not outshine terrestrial.

The day will arrive fairly soon when what they really need are HD simulcasts of their 2 main channels - and the other 2-6 channels (depending on what counts as a "channel") can't be that far behind. Yet they are basically committed to MPEG-2 SD broadcasts of 4-8 channels for years, if not decades, to come.

I know what I'd do (give people everything on satellite / whatever they can manage on terrestrial), but their platform neutral stance may stop them.

The challenge is as much political as technical.

Cheers,
David.

In the past there was enough bandwidth to give 7 megahertz per station, suddenly in the digital era there is not. While reading about D(VA)B, I get the impression that we're discussing how to fill one's ipod.

As far as I know they switched to a new encoder that is able to use CABAC and therefore they now can use a lower bitrate to get the same picture quality. Most other H264 HDTV channels still don't use CABAC.