Originally Posted by DSperber
Low-motion sports (e.g. The Masters) look gorgeous in 1080i, even from NBC.
I still find NBC's audio to be much too low (at least here in LA, on TWC), and CBS's to be MUCH higher (i.e. local highest!) by comparison.
The actual overall audio levels of the networks are very close. What makes the overall volume differ so much is the AC3 (aka Dolby Digital) dialnorm value. This parameter controls an attenuator in the AC3 decoder. CBS/CW uses -31db, which has zero attenuation. NBC uses -22db which has an attenuation of 9db. Fox uses -25db which is 6db attenuation. ABC does not transmit dialnorm to the stations so it's set by the station itself. ABC O&Os are around -27db to - 25db (4 - 6db attenuation). The default setting from Dolby is -27db.
Very few decoders allow the dialnorm parameter to be ignored, but on one that does the volume difference between stations is diminished, especially when going between CBS and NBC.
The dialnorm value is sent by CBS and NBC to their affiliates using metadata. CBS also uses the metadata to switch the stereo mode from 2 channel stereo to 5.1, and can do so on each program element including commercials. NBC used to do that but has stayed in constant 5.1 mode since the last Olympics, regardless of whether the show is 2.0 or 5.1. I don't know what purpose the metadata is serving right now on NBC since it doesn't appear to vary, but that may change shortly. CBS's dialnorm also doesn't vary. Affiliates of CBS and NBC that use the network metadata can alter their station encoders for a different dialnorm than what the network is sending. I'm sure both networks would frown upon that, but it would probably make for better consistency in a given market. That's only a pipe dream in major markets like NY, LA and Chicago as the CBS and NBC stations there are O&Os and have their hands tied.
The Masters is broadcast by CBS.
AFIAK, CBS O&Os are not multicasting. NBC O&Os generally have at least Weather Plus, some have more. Fox reserves about 15-16 Mb/s of a station's ATSC channel for its HD stream via their splicer.