AC3. I need to record it and decode it...

[cuttothebeat]

I have a couple of projects where after I have delivered the 5.1 discreet mix, they have been broadcast via satellite and therefore converted to AC3.

The mixes were simple and conservative and I think they would have survived the conversion to AC3 well. However, somewhere between me and the broadcast, I think the mix has been tampered with. The first time, it was somehow downmixed to stereo and no dialogue was present in the center speaker and no fx were present in the surrounds. The second time, music that was originally panned hard front left / front right was also coming out of the surrounds.

I want to record a feed from the set-top-box where these programmes are recorded so that I can try to work out what happened. I have no other option than this because there are so many people in the distribution chain and I am getting no help or answers from them!

What I need to do is this:

1 - Record the SPDIF AC3 output from the STB
2 - Decode to discreet wav files

Anybody have any clue as to how to go about this?

Many thanks

[networker]

If your mix downmixed without Dialog, it probably means that the metadata was telling the downconvertor that it was already a stereo mix...thereby taking ch 1 Left and ch 5 Right as if they were ch 1 and 2.

check your metadata.

[quadraphonics]

Neyrinck's AC3 tool will do this. You can feed the SPDIF into your I/O and assign it an Aux. Put the AC3 decoder on the aux and record the resulting output.

As for the issues it sounds as though you are only getting a Stereo/Dolby Stereo feed. The first being LoRo, where it is NOT being decoded through a PL decoder and the second being a LtRt which is being decoded (hence the music and stereo sfx information in the surrounds).

It isn't so much that it is being tampered with in the traditional sense (someone remixing for instance) it is more a by product of a broadcast distribution chain where the original 5.1 is not being rebroadcast or not being rebroadcast correctly.


Randall

[Doug the Brit]

+1 for Neyrinck!

It will also show you the metadata that has been coded into the AC3 stream.

-Doug

[Craig F]

taking the SPDIF out of the box to the SPDIF in should be fine, be sure to clock to the income stream (I have done this setup before but I used a DP564 for the decode)