Digital television is well and truly with us now and like any new technology there are pitfalls in buying equipment to enjoy this media.
Is it really any better than analogue television?  There is no doubt about that, it is a vast improvement.  The main benefits over analogue broadcasts are:

·    Better, sharper video (with spectacularly detailed video if High Definition)
·    Better, digital sound (with Dolby Digital 5.1 surround available on selected programs)
·    Extra content and channels (including SBS World News Channel, ABC2).  Each station has up to four sub-channels which in theory could broadcase separate programs.
·    Program information (electronic program guides that show what programs are to be broadcast).
At the moment if you have slightly snowy analogue reception you will most likely get good reception on a digital set.  Only the original picture is picked up on digital equipment, reflections (ghosts) are rejected so this also improves things.  You should not need to change the antenna as in each area the digital channels will be in the same band as the existing analogue ones.

Just like your digital mobile phone you will either have good reception or none at all.  The slowly degrading of the picture due to poor reception that happens with analogue signals does not happen.

All major Australian networks are now operating in digital format though as yet SBS does not have high definition equipment so all broadcasts are in standard definition, even from their high definition channel.

In regional areas not all have full digital coverage, while some have only ABC and/or SBS.
Some areas have digital only channels (for example, Tasmania) – meaning an entire network is available on digital broadcast only, with no analogue equivalent.
To find out which digital broadcasts are available in your area, visit Digital Broadcasting Australia’s Reception Locator.

Every network has to broadcast at least one standard definition channel at all times (the ABC and SBS have standard definition multichannels), and at least 1040 hours of high definition programming each year.

In Australia, High Definition is defined as a broadcast with a format of 576p, 720p or 1080i.

Seven, Nine and Ten use 1080i, while ABC uses 720p.& 576p is used by SBS. Regional affiliates follow the format of their metropolitan station – WIN and NBN use 1080i, Southern Cross Ten uses 1080i and Prime uses 576p.

What do these numbers mean?

1080i
The highest resolution used in the HDTV. 1080i stands for resolution of 1920x1080 pixels and the 'i' means that the video is being interlaced. Currently used by the 9 and 10 network with Channel 7 just starting.

720p
Medium resolution used in the HDTV. 720p stands for resolution of 1280x720 pixels and the 'p' means that the video is in progressive format. Used by the ABC.

576p
The lowest resolution for HDTV and consists of 576 lines, and the p stands for progressive.  This is really no improvement on standard definition TV.

Interlace
Method of smoothening the video picture moving by having double the amount of frames than the video's frames per second value suggests.

Basically, how the interlacing is done, let's say in PAL format, is that each frame is split into two separate pictures, which both are missing half of the picture information. The split is done by its horizontal lines. The PAL video contains 576 horizontal lines -- let's say that the numbering of these lines begins from the top of the frame being the line number 1. The frame is being split to half-frame A and half-frame B -- the half-frame A would contain lines 1, 3, 5, 7, ... and the half-frame B would contain horizontal lines 2, 4, 6, 8, 10, ...

So, when the video is shown with PAL that has frame frequency (fps) of 25fps, there are 50 "half frames" per second that are being updated. First comes the first full frame's "half A" that fills horizontal lines 1, 3, 5, .. leaving other ones blank (assuming that we start from a "zero state" that output doesn't have anything shown before we start counting this). Then comes first full frame's "half B" that fills the missing lines 2, 4, 6, ... and leaves the existing "half A"'s lines showing as well -- now we have the frame no.1 fully shown on screen. Then comes frame no.2's "half A" that then wipes off the frame no.1's "half A", but leaves the frame no.1's "half B" showing. So, now we have a mixture where lines 1, 3, 5, 7, .. are being filled by frame no.2 and lines 2, 4, 6, .. are being filled by frame no.1.

Progressive
Progressive or progressive scan is basically an opposite to interlaced picture.

In standard, interlaced analog TV, the picture on TV is changed 50 or 60 times (50Hz in Europe/PAL systems and 60Hz in most NTSC systems, including the American one), but the picture contains only every other horizontal line and the line between is left "empty" -- and the next frame then contains only the horizontal lines missed in the last frame. So, therefor in interlaced picture, at 50Hz frequency, the picture actually changes only 25 times per second (so its framerate is 25fps).  However, as the eye is slow to respond to change the picture looks better than a 25fps display.  This is why it was introduced in the first place.

But in progressive scan technology, every picture contains everything, so therefor 50Hz progressive scan video changes the picture 50 times per second, having the framerate of 50fps.

A couple of years ago there was some debate as to which was best, 1080i or 720p.  I can tell you, thirty seconds of viewing shows that 1080i is a clear winner.

Every station is required to meet a quota of at least 1040 hours of HD programming per year. For the commercial stations, these 1040 hours must comprise of native high definition programming. The ABC and SBS are given special conditions, and can count up-converted (meaning scaling up the standard definition to high definition, then broadcasting it in a high definition format) content towards their 1040 hours. However, even though the ABC doesn’t have to broadcast native HD programming – they still commit the resources and effort to do so – with much praise due to the operations team at the ABC.

The difference between 1080i, 720p, 576p and 576i
 
1080i is usually regarded as the highest quality format for free to air HDTV – it provides the highest vertical and horizontal lines of resolution, and is the international standard for HDTV production and distribution.

720p also is a great improvement over standard definition (576i), but has less vertical and horizontal lines of resolution than 1080i. The ABC uses 720p as it is less bandwidth intensive, meaning it can fit into a smaller space. The advantage of 720p over 1080i is that it is a progressive signal – meaning each frame is a complete, full resolution image – versus each frame being made up of two fields, which have to be somehow combined.

However, broadcasting progressively is only useful if the source is progressive – which isn’t the case for most programs – they’re usually supplied as 1080i negating the benefit of the progressive format.

Australia’s situation is unique, as internationally 576p is not recognised as High Definition, but rather as Enhanced Definition. 576p isn’t much of an improvement over 576i, as it has the same 576 lines of resolution, but is progressive rather than interlaced. The decision to allow 576p as HDTV has had much criticism from the enthusiast and technical communities – but we’re stuck with it for now.

576i is the format for standard definition television (SDTV), and is very similar to DVD (which is also 576i for PAL countries).


How can you receive High Definition television?

As a minimum, you need a receiver capable of decoding High Definition. This can include a High Definition Set Top Box to connect to your existing television, a television with an in-built High Definition tuner, or even a Digital Television Tuner card for your computer.  There is little point in connecting an old style (CRT - Cathode Ray Tube) television to a High Definition set top box.  If you cannot afford a flat screen then just purchase a Standard Definition set top box, which costs about $100 or less.  You will certainly have better quality TV than with the analogue tuner in the old set.

To truly experience High Definition television – you need a display that can display at a High Definition resolution and here you run into problems!  Many of the sets being sold in Australia are only 1366 x 768 pixels.  While this will display 720p (though not fit well) it cannot do justice to 1080i transmissions.  For Australian digital TV reception you need a display that is either 960 x 540 (for standard definition) or 1920 x 1080 (for high definition).  Even with the latter screen the images from 720p and 576p will be stretched to fit and will not look as good as if they were displayed on a smaller screen  You probably know this effect by looking at images on your computer  when viewed at more than 100% of their original size.  My advice is (unless spending lots of money is not a concern) get a standard definition display that is 960 x 540.  This displays standard definition broadcasts extremely well and as it is 50% of the 1080i signal these are also displayed well.  In a few years when most broadcasts are in High Definition, and sets are much cheaper, move to High Definition.  Update May 2009 - The price of HD sets has crashed so I now recommend buying a 1920 x 1080 set.  DON'T BUY TOO BIG!

Bigger is not always best!  We have a 37 inch (93cm) LCD display with 960 x 540 resolution (standard definition) and view it from 5 - 7 metres.  At this distance Standard Definition broadcasts look extremely good and High Definition ones look spectacular.  If you have a 65 inch (165cm) display viewing from this distance would be OK for High Definition broadcasts but Standard Definition would look pixilated and 'chunky'.  Remember, most broadcasts at the moment are in Standard Definition.  DVDs are only 576/580p and so would not look as good as on a smaller screen. A good rule of thumb for viewing distance is 4 times the diagonal screen size - for our 37" screen this would be 12.3 feet (3.75m).  Check it out yourself in a store - be sure to watch a standard definition transmission as most programs are still in this format.

Another consideration is High Definition DVDs.  This technology is very new and not many movies are available in this format.  In a few years when these are common-place then a 1920 x 1080 display will be essential as this is the resolution of this format.  They are in 1080p, which should be even better than the current transmissions of Channels 9 and 10.

With 1080i transmissions no other format can be transmitted so if no programs with this resolution are available, or no ads, demo tapes are run with various Australian scenes.  On Channel 9 with nice music, on Channel 10 with artificial junk!  If you want to compare various HD TVs in a shop ask to have them tuned to Channel 9 HD, you will then be able to see the difference between 1366 x 768 and 1920 x 1080 displays.  Remember, not all sets have the full High Definition resolution.

Which is best - LCD or Plasma?  You can get into arguments at any time over this.  Personally I prefer LCD.  Apart from the fact that they run cooler and use less power I think they look better.  A year or so ago they were not so good but they have finally come of age and will only improve from now on.

Beware of ads that say 'HD ready'.  They are definitely not High Definition sets.

The difference between 1080i, 720p, 576p and 576i


You can see from the above image how much a 720p image has to be expanded to fit onto a 1080 pixal screen.

With any new technology we are plagued with differing standards.  This could not be more of a problem than with DVDs.  There are so many different ratios used for movies that it is absolutely essential that when selecting a DVD player you choose one that can zoom the picture in small increments so you can fill the screen.  Our Panasonic unit has a very good feature, “Zoom to Fit”.  You tell it what your display is and ‘Hey Presto!’ the image fits.  Many units have a completely useless zoom feature of x2 x3 etc, you need to be able to zoom a bit at a time.  The diagram above from a Panasonic manual shows the variation you need to be able to cater for.  There is nothing worse than sitting down to enjoy a new movie you have just purchased to find it displays much smaller than the screen size.  Strangely enough many of the cheap DVD players have a zoom feature that does the job nicely but these players do not have high quality audio or video output and do not last.

UPDATE - May 2009.
Instead of getting better things are getting worse on the problem of resolution.  Today I looked at a catalogue from Big W and saw the following "High Definition sets for sale" -  42" Plasma TV - Resolution 1024 x 768 (this is a computer monitor, not a TV), 15.4" LCD TV - Resolution 1280 x 1200 (this is not anything!), 22" LCD TV - Resolution 1680 x 1050 (another computer monitor resolution).  This is complete rubbish that is being dumped on us.

There is a fairly good article in PC User, June 2009, that talks about digital TV.  One thing they do NOT mention is that most transmissions are still standard definition (920 x 540) and when viewed on a large (42" or larger) screen you have to be a long way back before the image looks much good.  The article says that a good rule of thumb for viewing distance is 3 times the diagonal screen size - for our 37" screen this would be 9.25 feet.  I would put this as the absolute minimum and would go so far as to say 4 times is far better.  This means for a 65 inch screen you would be 21.6 feet back.  You would need a big room.  Don't make the mistake of buying too big.
 
Links
DTV Forum Australia - helpful community of digital television enthusiasts.
Digital Broadcasting Australia - a wealth of useful information on Digital Terrestrial Television (DTT) in Australia, including reception advice.
Site Offline - over 400 screen captures of High Definition programs broadcast in Australia.
DTV Forum Australia - Discussion on all things relating to digital TV.
Cheap DVD Players Come At A Price - The Age - Digital Life.
HD TV Resolution Explained - Cnet


References:  High Definition television (HDTV) in Australia,  Smarthouse, Digital Television in Australia.

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