Tuesday, December 23, 2008

Digital TV: Goodbye Analog Snow, Hello Digital Losses

We don't have long to go until over-the-air analog television bites the dust, replaced with digital signaling on February 18. Watching televison the "old-fashioned" way (without cable) brings back fond memories of the aerial antenna on top of my parents house. I remember my Dad climbing up on the roof to move the antenna so we could watch Boston Bruins hockey games more clearly. It only took a few trips to the roof before we had one of those fancy motorized antennas with a controller on top of the set - no more roof climbing to redirect an antenna with one of those - just a twist of a dial......

Most of us have come a long way since those antenna days but there are still many in this country who watch television over-the-air. Realizing this, Congress did get out in front of the digital conversion a year and a half or so ago and starting offering $40 coupons (see www.dtv2009.gov ) consumers can use towards the purchase of a digital set top conversion box. Basically these boxes take the digital signal from the air and convert it to an analog signal that an analog TV can use.

Moving to digital has a lot of advantages including a 3:1 channel ratio - you'll have three digital channels for the equivalent of one single analog channel. It also frees up spectrum for new wireless communications services.

There are also some disadvantages though - most analog sets have 4:3 ratio screens while most digital programming is broadcast in wide screen format. This means analog set owners are going to see letterboxing - black bands at the top and bottom of screens. I think the biggest complaint though will be from those who live in areas where broadcast signals are weak.

Let's take a close look. Back when we were watching those Bruins hockey games we expected a snowy picture - if you're not sure what a snowy picture is - here's an 18 second analog transmission video I just shot:

A fuzzy/snowy picture with good audio - it's watchable and it is also listenable. Analog signals fade gracefully (as someone much smarter that me once said whose name I cannot remember). As signals get weaker the picture snows up but is still watchable. The audio is commonly good with weak audio signals - in fact you typically lose the picture before you lose the audio.

Digital transmissions are another story. Weaker signals will cause the picture to randomly lose pixels along with random pieces of audio. Here's a 20 second digital transmission video I just shot showing pixel and audio loss.

Pixel lose is scattered and occurs throughout the video and, if you missed it, audio is momentarily lost at around 5 seconds. Annoying and just about impossible for me to watch for more than a few minutes..... I'm changing the channel!

Over the air digital television is being pitched by many as a go-no-go service, with people saying you will either get the channel or you won't. From what I've seen this is not the case - there is an in between that is not very pleasant - those digital signals do not fade gracefully!

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