Thursday, January 15, 2009

Wall-E Blu-ray DTS audio glitches

The Blu-ray disc of Pixar's Wall-E experiences several brief DTS audio dropout glitches when played on a Lexicon DC-1 THX AC3 DTS preamp with the v2.01 firmware. The DTS audio plays flawlessly until about 18 minutes into the movie when the first brief audio dropout occurs. The glitch is very annoying and it happens about 20 times during the movie. The dropouts are repeatable and they always happen at the same locations. When it happens the Lexicon loses lock on the 5.1 DTS signal, switches to 2ch 48K PCM, and then reacquires the 5.1 DTS signal all in a fraction of a second.

The Lexicon DC-1 is a 12 year old surround pre-amp that has played thousands of AC3 and DTS movies on LaserDisc, DVD, and Blu-ray without any problems. This particular Wall-E Blu-ray is the first disc that has had any audio decoding problems. It's surprising considering the amount of time, the number of different discs, and how fast technology has changed in pasts 12 years. No audio decoding problems until the Wall-E Blu-ray disc. Amazing actually.

The audio glitches go away if the Sony BDP-S350 Blu-ray player is instructed to decode DTS internally and output 48K PCM 2 channel surround. So the problem is not the player or the Wall-E disc but the ability of the Lexicon to decode the DTS stream.

The Wall-E packaging says that the audio is 5.1 DTS-HD MA (master audio) when it is actually 6.1 channels. The DTS-MA on Wall-E uses a legacy 1.5Mbps DTS core that since it's 6.1 is DTS-ES (Extended Surround) which has six discrete channels. DTS-ES uses a core + extension design where the extra rear channel uses optional packaging flags that in the past haven't caused the Lexicon DC-1 any problems. Somehow this incompatible DTS-ES stream is encoded slightly differently.

The DTS website says this about the 6.1 DTS-ES core + extension:
So, if you have an older DTS-capable receiver, it will “ignore” any extensions and just decode the core — ensuring you of compatibility and very high quality.
Unfortunately that doesn't seem to be the case with the Blu-ray of Wall-E and a Lexicon DC-1. So the only solution is to listen to Wall-E with a 2 channel PCM downmix that lack dynamics, bass, and discrete channel steering. I guess it is time to upgrade my Lexicon DC-1.


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