[This was a Geekzone blog entry that didn't get much response, so I'm re-posting here. Might also have some relevance to this HD/.ac3 thread: http://www.geekzone.co.nz/forums.asp?ForumId=83&topicid=21288 ]

For years now on analogue and cable free-to-air TV I've been hearing a dodgy audio artifact on broadcast US TV shows - the likes of Six Feet Under or The Sopranos. It's most noticeable on music featuring sustained solo notes on violins or flutes and is best described as a regular (1 or 2 Hz-ish) momentary jump, bump or gap in the audio. To my old-skool ears it sounds as if someone stopped a 1/4" takeup spool and then let go, bouncing the tape as it comes to rest.

I think I've figured out what it is, from watching Battlestar Galactica Season 3 on PAL DVD. There's an option to choose a 5.1 or stereo soundtrack on these discs. The stereo is sped-up from the original 24fps to 25fps, but pitch-corrected back down. The 5.1 is sped up *and* pitched up from 24 to 25 - just like speeding up an analogue tape.

The artifact I described is exactly what I hear on the stereo DVD soundtrack, and is unbearably bad, especially on the BSG theme tune - that plaintive solo wind instrument and female voice.

Obviously it's a rough-and-ready realtime effect of pitch-correction and speed-adjustment of the soundtrack. It drives me nuts BECAUSE IT'S SOOOOOO BAD AND NO-ONE COMPLAINS.

Well, until now, obviously.

Does anyone know what I mean and/or can shed light?

Cheers,
Tom