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While watching some freesat recently, we noticed that the quality was terrible. On closer investigation, we discovered that people using freesat for standard definition are being short changed, and it’s all down to the bit rate of certain freesat channels.
We’ve always said, good standard-definition TV can look really good, even on HD televisions. So why, you might ask, why does digital TV look like something YouTube would be ashamed of when we were promised crystal clear picture and sound quality? We think the answer simple — and predictable — it’s all down to money.
In the current climate, we’re all acutely aware of how a lack of dosh can cause problems. In TV broadcasting, the specific problem is that sending a signal over the air either via a terrestrial network or from a satellite orbiting the Earth costs quite a hefty wedge. To reduce the cost per channel, companies squeeze more on to each multiplex or, for satellite, every transponder. The more channels you squeeze in, the lower their bit rate must be, and that has a direct impact on the picture quality. So, if money was no object, it’s fair to assume the quality of both Freeview and freesat would be much better.
Freeview is quite limited in bandwidth because there’s only so much space in the spectrum. That places some restrictions the quality of broadcasts. In total there are six multiplexes in the UK. Depending on the modulation system used — there is a choice of two, 16 and 64QAM — they can each provide between 18 and 24MBps. A move to DVB-T2 in the future will increase the maximum to around 35MBps, but that won’t be compatible with existing receivers.
Satellite is different though: there’s much more space available and it’s also considerably cheaper to broadcast via the Astra satellites — the main reason is you need just one satellite to cover the whole of the UK, whereas a transmitter network consists of dozens of expensive masts. Despite this, it appears broadcasters are generally doing a better job with their over-the-air Freeview broadcasts than their extra-terrestrial freesat ones.
So, which channels look the worst and why? Channel 4 illustrates two issues; the first is the frame size used in broadcasts, the second is the bit rate. If you compare Channel 4 on Freeview to the version available on freesat, you’ll notice that the average bit rate is much lower on the freesat version. It’s also using a smaller frame size on freesat: 544×576 pixels compared to 704×576 on Freeview. ITV is guilty of the same thing, with a freesat frame size lower than its Freeview version.
Only the BBC manages to keep the frame size the same across both platforms, and the data rate is also comparatively high, although there are times when it drops to startlingly low levels.
Annoyingly, it also appears that Channel 4 broadcasts its channels twice. One set of channels, for freesat, are unencrypted and another set, which are encrypted, are for its Sky package. The Sky channels appear to have a slightly higher bit rate, meaning if you have a Sky viewing card — either a paid-for service, or its free system — you’ll be getting a better quality version of the service than freesat viewers.
With HD on Freeview and freesat far from prevalent, we’re stuck with picture quality that sucks on some channels. So while we’re waiting for HD, couldn’t we at least have channels that have an appropriate resolution and bit rate? Is it really so much to ask? –Ian Morris
