[georgia]

collection of a couple rants of mine in the past:

HDnet normally wants a digital video tape with LtRt and DOlby-E. The DOlby-E stream must be laid on the tape so that the audio ON TAPE is in sync with the video. So, depending on the frame rate of the video tape you will need to off-set the audio so that after passing thu the encoder the audio is in sync ON TAPE. The encoding process places an amount of delay on the output signal due to the encoding time. Additionally, during decoding of the DOlby-E stream the audio will be once again delayed. Normally you can delivery in sync ON TAPE or in sync AFTER the decoder or even out of sync by not doing any delay time adjustments. It depends on the delivery spec. Again, HDnet normally wants it in sync ON TAPE because they engest it to a server without decoding so all the media on the server is video+audio sync'd.
The same is true for an AC-3 delivery. Also note, that at 29.97 there is about 1 frame of offset for the encode process and 1 frame for the decode process.
DOlby-E is editable since is is a FRAME based delivery medium.. DOlby-AC3 is a linear digital stream. You cannot edit the AC3 stream ( ok I actually have a couple times in an emergency, but its a crap shoot as to getting the punch in and out clean enough to work sonically and meet QC requirements. ( Don't try this at home folks we're trained professionals... )
DOlby E is used to broadcast production transfer and can be decoded and re-encoded any number of times without loss or problem. DOlby-AC3 cannot be ecoded and reencoded without significant loss of quality. DOlby AC3 and DOlby-E can support broadcast delivery up to the cable head or brodcast local center. From there AC3 is the delivery methodology for the final audio to the consumer. ( Like your cable box )

If you are trying to FIT a mix into a broadcast require spec, lowering the mix is not the right answer. It will take the lower end SFX and ambiences and drop them 3 db as well. You need to remix to meed the DIALNORM reqirement. The biggest problem in all this is that Discovery and almost all the other major broadcasters are using DIALNORM backwards. But until they get it right we are forced to mix to a set DIALNORM setting.. The LM100 DIALNORM methodology is as follows: Whatever channel is selected for monitoring, that channel is monitored using the LM100 and the custom software within the LM100 that reads the Dialogue level. As it does this it averages over the duration of the program. It also has the ability to differenciate between Actual Dialogue and non-dialogue events on the selected channel. Once you have the DIALNORM (actual) you can then encode the overall audio as DOlby-E or DOlby-AC3 with metadata. Part of the metadata is in fact the DIALNORM setting. The DIALNORM metadatasetting should accuratly match the ACTUAL DIALNORM average. If this is done, then no matter what the level of the mix really is, the level between all the mixes on a program channel will be raised or lowered to meet the broadcast DIALNORM setting. What is happening in reality is the broadcasters are forcing you to MIX to a specific DIALNORM setting instead of using DIALNORM properly. So if you just lower your mix total level you will probably lose a lot of the quiet SFX and Ambience areas and this may be not what you or your client wants. You would be better off remixing the spot or program to the correct the DIALNORM setting.

We do this alot with outside facilities for just this reason. In fact one of the things we are doing more and more of is DOlby-E and DOlby-AC3 mastering for smaller houses for this very reason.
Seems i'm at DOlby more and more fixing this stuff before it goes to the Broadcast company. go figure.

this is not about the mixers, sound designers, re-recordings issues, editing, avid editors or the like. 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.

Whats supposed to happen is the following:

You don't have to set a spec of -27 diagnorm. WHAT YOU DO NEED TO DO, is to set a spec that says the diagnorm meta data MUST BE EXACTLY what the actual Diagnorm really is. If the metadata and the acutal DN do not match kick it back in QC.
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.

cheers
geo