#1003040 - 07/23/05 09:15 PM
Dolby Digital TV Audio
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Eric Day
Senior Member
Registered: 08/23/04
Posts: 65
Loc: Austin, TX
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I'm sure some of you pay attention to what is broadcast over TV/Cable/Satellite in 5.1. Have any of you noticed some of the issues with the 5.1 broadcasts? I know this is being worked on as I write, but some channels have weird things going on -
I've been watching the Tour de France lately on Outdoor Life Network (OLN), and I noticed that this particular channel is broadcast in Dolby Digital 24/7. They must encode everything for broadcast somewhere. This is the only channel I have with Digital Cable that is Dolby Digital on my receiver 24/7. Here's my question - I know that TV can be broadcast in Dolby Digital 5.1 and 2.0, but why is it that sometimes the shows or commercials are 2.0 (left/right only), sometimes it's L,C,R (just the 3 front channels, nothing else), and sometimes it's 5.1 discreet? The 5.1 stuff may be surround encoded as Pro Logic II and delivered to the station as stereo, then the surrounds chime in almost like discreet channels. Some of the car commercials have surround effects and 5.1 music. It's just bizarre. The audio is all over the map, there's no consistency. The worst thing is that the surround channels have distortion and fuzz in them during the shows and commercials. Sometimes all the audio is in the center channel only, and there's nothing in the mains or surrounds. Now HBO has a successful 5.1 Dolby Digital broadcast going for select shows and movies, and it always works, but what is happening to the Dolby signal for OLN? It's even a good 15dB too quiet. I have to turn my receiver up really loud just to hear it. Something's wrong. I don't mean to pick at their broadcast or say someone is doing a bad job, I just wonder if they know. Is it in my cable market where the issues begin, or is it in the Dolby E transmission. I'm curious why this feed is so bad.
Right now a lot of shows are delivered to networks in Dolby 5.1 (as Dolby E encodes?), but the commercials are stereo, so the Pro Logic kicks in on home receivers. Is the plan to go 100% digital like OLN, where the Dolby decoder never clicks off? Maybe just my cable market has these audio issues, but it doesn't seem like it, because all the other channels I get with Dolby content sound amazing. CBS, Cinemax, HBO, etc.
Any thoughts? Anyone in Europe catch the Tour de France and have any input on the audio over there? Was it a 5.1 broadcast?
Hmmm...
Eric Day
Austin, TX
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#1003041 - 07/24/05 07:59 AM
Re: Dolby Digital TV Audio
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Neil Wilkes
Gold Member
Registered: 07/06/02
Posts: 514
Loc: London, UK
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Not too sure about the exact answers here, but there may be a solution if you think about the type of encoding used.
Dolby Surround (as was)and Dolby ProLogic (as it became) was an analogue matrix encode to LRCS.
Dolby ProLogic II is also an analogue matrix encode, in 5.1 this time, but still essentially an analogue matrix process that plays back according to your hardware. Despite the incremental naming protocol, it is a totally different process to Dolby ProLogic, as it uses a delay line & comb filtering to get some life into the surround channels and does not give you dual mono output.
DD can be from 1/0 to 3/2 with the .1 channel available from 2/0 upwards. It is a digital discrete system, and not to be confused with the analogue matrix versions of Dolby Surround and DPL II.
The problem, I think, is that some stations still use analogue sound, which necessitates the use of DPL or DPLII, as DD can only be fed digitally.
Once the analogue stations are all switched off, you will see everything go to DD.
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