capture my mix off broadcast for comparison?

[alexeymohr]

I'm a TV mixer and I do shows for a few different networks. I've always been frustrated by listening back to the show on broadcast and feeling like the mix is not the way I left it.

I'm trying to devise a way to capture my mixes off broadcast and bring them back into Pro Tools to compare and try to figure out just what the broadcast chain has actually done to them. I'm mainly interested in capturing the 5.1 mix, which means dolby digital I'm assuming. I've done some looking online for capture options, but this turns out to be much trickier than I thought!

I'm hoping to find a way to capture episodes off my DirecTV DVR with full 5.1 audio, and perhaps also capture it off over-the-air rabbit ears as well. I'm looking to accomplish a few specific things:

1) identify the type of audio being broadcast; I'm assuming it's still mostly dolby digital AC-3, but I wonder if anyone is broadcasting Dolby TrueHD, E-AC-3, maybe DTS, or maybe even some other format?

2) capture that audio exactly as broadcast, then get it into Pro Tools for comparison to the mix stem that I delivered initially. I'm sure that requires certain conversion tools to get from encoded AC-3 back to PCM audio in .BWF format.

3) And here's a CRUCIAL step I would love to achieve: read all of the dolby metadata being sent with the broadcast audio. This is the place that I believe the most molestation of the mix is occurring. There are a ton of parameters that can be set in dolby metadata, and I want to see what choices are being made by broadcast to best understand what's being done to my mix.

So has anyone ever set up a system to accomplish this? Does anyone have thoughts on good capture hardware, ways to bypass HDCP to get the audio out of HDMI, good software to capture the AC-3 and/or convert it back to .BWF files to be imported into Pro Tools, and software to read the dolby metadata?

[Bob Olhsson]

I was part of a group that recorded the SPDIF stereo output of cable boxes around the country to try and figure out why mixes often didn't sound right. We found a combination of stations applying additional processing and the widespread use of cheap knock-off Dolby decoders by cable companies.

[BScout]

It's easy but slightly expensive.

To get the audio out of the HDMI, you can use anything with a S/PDIF optical out (say your TV) and set it to bitstream so that it doesn't decode.

Then you can record that output (but remember you'll need something that can do asynchronous clocking or you need to temporarily make that incoming stream the clock master.)

Next you need to decode it. Neyrinck and Minnetonka Audio both have plugins that can do this. However Minnetonka's has to have the transport active while Neyrinck doesn't (which means if you input monitor in Pro Tools with the Neyrinck plugin on the input channel while passing the signal in, it will actively decode with the transport not moving.) They both read and display the metadata info too.

Big thing is you cannot adjust the s/pdif signal when bitstreaming AC-3 in anyway before it goes through the decoder or it won't decode (no re-clocking/sample rate conversion, no gain level changes, etc.) If you have auto-SRC on your inputs, turn that off because even if you aren't sample rate converting, it still messes up the stream enough to keep it from decoding.

Also, be careful not to hear the undecoded signal because it is loud/noise.

The other option (which I do) is use a Dolby DP564 which can decode and send out a digital version via AES of the decoded signal locked to a separate system clock (most of the earlier Dolby decoders only returned analog or couldn't be reclocked). There's just a bunch of wiring standards you need to deal with (AES3id) to make this work but if you have AES inputs (6 or 8 channels--for EX) on your system, you can return a proper digital audio decoded back into Pro Tools from the DP564 while keeping your master clock normal.

But doing all of this isn't cheap so depends how much you care.
(I haven't checked terrestrial digital but Netflix has been 100% bit perfect to what was sent to them for projects I've done.)