Dolby Lm100s measure Dialogue levels with a sliding window of time.
heres a link to the LM100 manual that talks about this.
http://www.dolby.com/assets/pdf/tech...iew.Manual.pdf
here's another about levels like Dialnorm
http://etvcookbook.org/audio/dialnorm.html
Some personal rants about Dialnorm....
If in fact this were accomplished with:
a commercial at a true DN -20 and metadata DN set to -20
a show at true DN -29 and metadata DN set to -29
a commerical at true DN -19 and metadata DN set to -19
When each is played back with the proper setting the levels will be consistant with each other.
The system
What screws this up are the folks not using DN correctly, by checking the level of their show / commerical and then setting DN to -31 when the true DN is -12. ( or whatever ) The whole concept of Dialogue Norm is to tell the system that the show is +/- and automatically adjust it to resolve the differencial to a standard level. At least thats what its supposed to do.
1. the mixer/client sets the appropriate metadata for the audio program being created by checking dialnorm. these are set to match.
2. The resulting audio program, together with metadata, is encoded as a Dolby E stream and sent to the broadcaster.
3. the Dolby E stream is decoded, checked, and adjusted as a matched program/metadata pair, reencoded as Dolby E, leaves the studio and goes to Master Control, where bunches of Dolby E streams are decoded back to their individual audio/metadata sets.
4. The audio program/metadata pair that is selected is sent to the transmission Dolby Digital encoder, which encodes the incoming audio program according to the metadata stream associated with it.
5. The metadata and the broadcast encoder, as well as the home decoder work togther to deliver the audio so that my decoder controls the levels for the commercial, or show. each using the metadata carried within the individual segment. OR in the case of the broadcast company decoding the final signal and sending it out to my crappy TV, the metadata once again keeps all the various items within the same program level at the broadcast head end.
Oh, my decoder says
"this is supposed to be diagnorm of -27 but its diagnorm of -10...oops droppin' down a bit... ahh thats better...
oh... look this one is diagnorm -30 oops lets kick it up a little... ahhh.. much better.
of this one is JUST right at diagnorm -27 cool... I can take a beer break."
bottom line is the DOLBY-E stream should be mixed to what the client or mixer wants.. Then check the dialnorm, then match the Metadata. Then encode properly in DOLBY-E the mix in DOLBY-E is NOT modified at all. The Metadata defines the method in which the mix is heard at the end of the pipeline. So the DOLBY-E stream with meta data is delivered to the Broadcast head, transfered or re-transmitted to the local cable or other broadcaster and decoded with metadata. the metadata is supposed to be passed the the final DOLBY-AC3 stream during the re-encode and the mixes are adusted by the broadcasters dialnorm setting so whe you receive the mix at home and you decode it at home OR its decoded and sent analog, the mixes are all adjusted dynamically to meet the broadcasters dialnorm setting. If your dialnorm is low or high the mix is adjusted so the listening community just hears a nice standard level across Ads and Programs.
THe reason for the LM100 is to provide the customer with an acceptable product that does not make them hit the channel changer and go to a competitor. LM100 specs, or actually, Dialog norm specs provide for a means to control the level of a broadcast stream in such a was as to allow a listener to sit down, turn on the TV, set the level, and enjoy the TV shows. If the specs are met for dialnorm, the listener at home does not have to raise the volume for a quiet show, and then dive across the room for the remote, while ducking incomming tweeters, when the commericals or another show starts.
Although dialognorm is being misunderstood by the broadcasters, and misused, it still works the way its being stated in the broadcast specs. dialnorm can be checked in 2 ways, there is a float window of 10 seconds (i think.. it might be up to 30 secs i'll have to recheck that)... and it can check a show from beginning to end and offer an average. If you take the average and set you dialognorm meta data to MATCH the actual dialnorm from your show. AND, if everyone else on the broadcast steam in question does the same thing, the broadcaster and set top box manufactures can set a level ( lets say -27 ) that works: and no matter how loud or quiet you mixed your project. The level is adjusted up or down to MEET the dialnorm directed by the broadcast stream, set top box, or dvd player. Thus all the programs are the same level while you listen at home.
One of the problems we are trying to overcome at present is the direction the Broadcasters are taking, forcing a delivery of dialnorm to be -27. This works, but its not the way its supposed to be. Dolby is setting up a ad-hoc standards committee including broadcasters, engineers, post facilities and the like to work on this and other level based delivery issues. What the broadcasters SHOULD be doing is forcing their QC department to simply check to assure dialnorm meta data = dialnorm acutal... AND, of course, specifiying in the delivery specs that, we as content providers, match our dialnorm Meta data to Actual dialnorm on our deliveries. The problem is that it means the broadcaster has to run everything through once to check QC instead of just spot checking some random area in the mix.
rant off....
cheers
geo