AC3 audio is VERY low compared to apples menu presets

Question

AC3 audio is VERY low compared to apples menu presets,
The original aiff files are at a good level, concert footage professionally recorded, nothing peaking, nothing too low.
THe AC3 is at minus 10DB on the vu meter, the aiff peaks at 100.
The apple menu music, which are .mov files, peek at plus 1-2.
My old version of compressor did not do this.
I do not have enough room on my disk for all AIFF but I do want to use the Apple Menus and provided music.
Any thoughts?

Answer 1

You can increase the Ac 3 "reference level" to 0 dB (it should be -27 dB)
Reference level? There is no such thing - I believe you are referring to Dialog Normalization, and it is extremely unwise to set this to zero... it is most certainly not a good way of increasing the overall volume of the file. -27 happens to be the application's default value, but it in no way means it should be set to -27. There are a few factors you need to consider when using AC3 encoding...
The DNV setting is the amount of attenuation that the file will get, according to a formula:
attenuation = 31 + DNV setting
Therefore if you set the DNV to be 0 you will alter all AC3 streams by 31 Db, which is enough to make it unplayable without serious distortion:
0 = 31 + (-31)
If you want to get the exact same audio levels out of A.Pack (or Compressor 2, if you are using that) then your DNV setting should be set to -31. This means there is absolutely NO attenuation to the file, meaning you get the same levels out as went in...
What I recommend here is to edit the audio in an application such as Peak and get it sounding exactly as you want it. When you encode to AC3 set the DNV to -31 and set the compression to 'none' (not film standard or anything else, there's nothing worse than badly applied compression). These settings then give you a basic output which is nearer to what you start off with. The other setting much talked about is RF Overmodulation protection. This is useful to turn on if you think the player will be sending the output signal to an RF input on a TV rather than through scart or something else. It certainly used to be the case that such signals were boosted by 11db, causing overmodulation. The setting is a way of preventing that hapening, but as more and more folk have stopped using RF as an input it makes sense to turn it off. If in doubt, turn it on, but listen to the output file and see if it is acceptible.
As for the basic bitrate, for a stereo file, lower it to no less than 192kbps.
Now, if you want to run a few tests, then keep all the settings above and encode the same 10 second piece of audio. Change the DNV to -31, then -20, then -8 and then 0 and play the resulting files back and listen to what happens each time.
Head over to http://www.macprovideo.com and download some of the tutorials there for A.Pack. They have been created by Martin Sitter (who has helped and guided me more than once) and will give you a far better understanding of AC3 encoding than anything else I can think of. You will pay for them, but it is a wise investment if you are at all unsure of how to get the best audio onto your discs. Let's face it, audio accounts for at least 2/3rds of the experience when watching TV - it is as well to get it right.