Sound question CATV DTV

[Jimdish255]

I have both DTV and my tuner card hooked up to a CATV coax. While watching various programs the sound (goes through my Denon AVR-591 amp) changes from 5.1 to stereo depending on the show/commercial. I generally record late-nite US programming and find that I get 5.1 for Kimmel and Fallon, but Leno and Letterman are pushing just stereo through both the DTV box and the Laptop tuner (NPVR). There is also an OTA antenna in my attic that gets the Connecticut NBC affiliate and Leno goes center channel on the antenna fed through the DTV OTA tuner, but the NY NBC "local" on the Sat is stereo.

Here's the weird thing. Both GOM Player and Mediainfo show a 6 channel audio stream:

(Mediainfo)
First audio stream
384 Kbps, 48.0 KHz, 16 bits, 6 channels, AC-3

If it were just the laptop (CATV) I would think there is an AC3 Filter setting to fix it, but it's the same watching on the DTV SAT so I'm thinking the 6 channel info is either misleading, or the receiver and DTV box are somehow not reading certain formats properly. As I said, other shows, movies and commercials have great sound but I wonder about these.

Any ideas about this or do you think I might get lucky calling DTV and asking a sound related question?

[Lao Pan]

Here in the UK Freeview HD often broadcasts Stereo over aac 5.1 - with 4 empty channels - annoying as no software or AV Amp can fill the empty channels as is possible for a pure stereo output.
I expect this is what you are experiencing.

[Jimdish255]

Thanks for the reply. I just got some advice about trying different sound modes on my receiver that would produce for a "simulated" 5.1.
It still seems odd that a major show is produced in a sound mode my receiver can decode from an OTA antenna, but both SAT and CATV providers are sending a stereo signal from the NYC affiliate? Then the show that follows goes to 5.1.

I've got a lot to learn but I'm determined to figure it out. Thanks though for a possible explanation I'll follow up on it..