Recently we bought one of these "set-top box" thingys that converts digital TV broadcast to analog so you can view it on analog TV receiver. The first thing I noticed after setting it up was that the sound quality is bad, maybe as bad as Gameplaya's Lame custom commandline! I mean, I can hear a lot of lossy compression artifacts. So my question is: does these artifacts originate from the set-top box internals (so a better set-top box would have better sound quality) or are they "part of" the digital TV broadcast? If they are part of the broadcast, what codec do they use? MP2 at 160kbps? (if they are part of the broadcast, too bad that the analog broadcast, which has better sound, will stop in like 2 years )

From what I've read, you're pretty close. :/

I presume you are talking about digital terrestrial TV as covered by the DVB-T standard. On the video side DVB-T is fundamentally MPEG2 based (although some countries have been using non standard MPEG4 variations). Curiously enough there are no standards for the audio side, most countries just use MPEG Layer II audio although you could just as well use MPEG AAC or Dolby AC-3.

The bitrate used is variable and is a trade off between quality and the number of channels per multiplex, unfortunately managers tends to cram as many channels in as possible so that both the video and audio come out in worse quality than they would have done via analogue TV.

To cap it all most DVB is cross coded in realtime from another source which is probably compressed itself. Therefore you end up with a multiplication of compression artifacts and poor encoding as the encoder can't use computationally expensive optimisations. This is much more of a problem for video than it is for audio as the computing power to compress audio to high quality in real time has existed for some time now.

Im in the UK and I just had a look at the main Freeview channels using the tv card in my pc and all where using either 192kbps or 256kbps apart from Film 4 which was using 160kbps.