All posts by Mike Dimmick
Below are all of Mike Dimmick's postings, with the most recent are at the bottom of the page.
M W Hodson: S4C Clirlun was included in Channel 4's original application for HD capacity on Freeview. My best guess is that Channel 4 HD will replace S4C Clirlun.
Channel 5 have twice been allocated capacity on Freeview for an HD service, and twice failed to launch. The first time, they left some aspects of their bid unconfirmed and failed to eventually tell Ofcom what those details were. The slot reverted to the BBC, who launched BBC One HD.
The second time, they reported that they would be commercially unable to launch. The fifth slot reverted to the BBC, who this time used the space for 301HD for the Olympics; it was then given to Channel 4 for C4 PG Extra during the Paralympics. We don't yet know what service will launch permanently in this space, it being expected that the BBC can't afford to run 301HD indefinitely.
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Squonchy: Check the specification on your box, but MPEG-4 Part 10 AVC (aka H.264) is not required for receiving Standard Definition television in the UK (yet), so it is unlikely that SD-only Freeview equipment supports it. Freeview HD boxes must support it as it is used for HD TV, and it will be used for the Northern Ireland mini-mux, which launches in October.
MPEG-4 is made up of a number of parts, and Part 10 was the *second* video encoding specified. However, it is very unlikely that Greece will be using MPEG-4 Part 2, the first encoding, as it is barely any better than MPEG-2 Part 2, as used for SD over here.
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Paul: Digital UK expect you to be using the Skinningrove repeater transmitter, rather than the main Bilsdale transmitter. You don't have line-of-sight over the cliffs.
The Skinningrove transmitter will be using different, slightly higher, frequencies after switchover compared to before. If you have reception problems it may be worth swapping the aerial for a group C/D or wideband design.
Skinningrove does not yet transmit ITV1, Channel 4 or Channel 5 in digital form. They will be turned on, along with the HD services, next Wednesday. The new services are expected to be available from mid-afternoon: see Digital UK - Relay transmitter switching times for updated information on the day.
If the problem persists after switchover completes, or for reassurance that the local transmitter is working properly, contact Digital UK on the number on their website.
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paul: Some equipment has two sets of channel memory, permanent and temporary. When the permanent memory is full, it starts putting new channels in temporary memory, which is lost when you switch off.
Make sure you are doing a full clear-out of the channel list before starting retuning. Check TV Re-tune for instructions for your TV, or look for the 'First-Time Installation', 'Factory Reset', 'Default Setting' or 'Virgin Mode' options. This option may be in the Software Update or System menu rather than in the tuning menu.
If that doesn't help, your TV may just not have enough memory for all the channels. If you can, use the manual tuning feature to just tune in the multiplexes you want, from the best transmitter - some equipment may store two copies of some channels if they are receivable from more than one transmitter. Other people have reported success by manually tuning the multiplex with the most channels, then deleting unwanted channels from that, and repeating with the next most, and so on.
Do check that your TV is not on the list of equipment with known tuning faults: see http://www.digitaluk.co.u…tnit . If it is, use the information there to contact the manufacturer.
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Ronald: The transmitter at Sutton Coldfield has carried HD since 21 September 2011, and The Wrekin since 20 April 2011, covering the first postcode you gave. The second postcode falls into the Wenvoe service area, which launched at the end of March 2010.
As Dave Lindsay says, the most likely explanation is that your TV is not compatible. It must support the DVB-T2 transmission standard, not just DVB-T, and it must support the MPEG-4 AVC video encoding, not just MPEG-2. The easiest thing to look for is the Freeview HD logo.
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Catherine O'Malley: Chances are that the conditions were right to receive a strong enough signal to be detected, and that your equipment is one of those that stores the first version of a service it finds, rather than the best available.
The Freeview guide is being updated tomorrow lunchtime to move some channels around, to make more space for the future, and change the prominence of some channels. Yesterday is swapping with Dave, moving down to number 19. I suggest you retune again after midday. You should use the same retuning process you used at switchover - see TV Re-tune for manuals and retuning guides for selected equipment.
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@bored now: The BBC bid makes sense as the money for it has already been top-sliced from the licence fee. If the BBC win, they will be able to combine the management effort with their existing multiplexes, and not waste any more licence fee money than necessary (possibly allowing some of the ringfenced money to be diverted back to BBC content spend, where it belongs.)
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Mark Fletcher: Rubbish. Unless Claude Shannon's Theory of Information is wrong - which is unlikely - the maximum bitrate achievable for the conditions that the HD multiplex currently operates in (8 MHz channel, minimum 17.8 dB signal-to-noise ratio for a random white-noise channel) would be approximately 47.27 Mbit/s. The HD multiplex currently achieves 40.21 Mbit/s. The improvement is subject to diminishing return - you need more and more processing power to handle the error-correcting codes that deliver the increased capacity. Low-density parity check (LDPC) codes already approach the Shannon limit (to 0.04 dB) with block lengths of 10 million bits - rather longer than the 64,800 bits used in DVB-T2.
The only way to increase capacity further from the same bandwidth is to adopt multiple input-multiple output (MIMO) transmission. This requires the end customer to have multiple aerials pointing at the same transmitter, and the broadcasters to install multiple transmitting aerials and transmitters. Basically, it means doubling (trebling, etc) the costs, to both transmitters and receivers, for less than double (treble) the throughput.
The compression ratios may well increase, but it's worth pointing out that it's taken 14 years for the compression ratios on Freeview to allow twice the number of channels per multiplex as at onDigital's launch - and many channels on the multiplexes that do have 12 simultaneous channels are now running in reduced resolution (544x576 rather than the proper 720x576) and that many viewers consider the compression artifacts unacceptable. MPEG-4 AVC is more efficient than MPEG-2 Visual, but HD channels still average around 8 Mbit/s compared to an SD channel's 2 Mbit/s, with five times as many pixels to handle. Call it an improved efficiency factor of 20%, which allows for the fact that the level of compression artifacts (and the acceptable level) on HD at present is low.
Ultra HD would be expected, for 4K mode, to deliver 4.27x the number of pixels compared to HD. Let's say the next-generation compressor can again deliver 20% improvement compared to AVC. You still need 3.4x as much capacity as for an HD channel. That means probably not achieving even two UHD channels per multiplex.
For a technology comparison, yes, LTE Advanced (the 4G mobile phone standard) is quoted at over 1 Gbit/s, but that is achieved through wider bandwidth, up to 100 MHz, about one-third the width of the entire Freeview broadcast spectrum; deeper MIMO, up to 8x8 (8 transmitters, 8 receivers); and that is the best possible performance for receivers very close to the transmitter. In practice users will be much further away from the cell tower and won't get anything like that performance. You're also sharing the capacity with other users. 802.11n Wi-Fi similarly gets its best capacity at far higher signal-to-noise ratios, using 40 MHz bandwidth, and using MIMO techniques. DVB-T2 gets better bitrates (bits/sec/Hz) than either if you consider the SNR available, the bandwidth available, and the fact that as currently deployed, it only uses single in-single out; it can use deeper error-correcting codes, and greater modulation depth (256QAM vs 128QAM, for example), because it is expecting fixed-position mains-powered receivers rather than battery-operated mobile devices (so can require more computation power) and doesn't have to accommodate rate-adaptation because it is broadcast, rather than trying to adapt to the best rate for the targetted mobile device.
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Monday 17 September 2012 5:57PM
des: Because the digital transmissions *replace* analogue ones, it is not possible to run continuous test transmissions. There may, periodically, be analogue shutdowns overnight to allow digital test transmissions.
See
Digital UK - Planned Engineering Works for notice of any engineering works. It's likely that this would be listed under Limavady rather than Strabane itself.
Note that when digital test transmissions *have* been broadcast, they are deliberately broadcast without any Service Information, meaning that receivers will not pick up any services if retuned at that time. This is to prevent those boxes which do automatically retune overnight from mistakenly deleting their current set of channels.