Windows 7 Pro 64-bit.
Audacity 2.1.0.
I presume the painfully slow Export to AC3 is due to the conversion, while exporting, from PCM to AC3? In which case, there is very little that can be done to speed things up?
This is a painful process, since using a chain to amplify to a specific level doesn’t work, seeing as the parameter is Ratio, which depends on the levels in the file being processed. And you can’t normalise multitrack.
What exactly is your question? What are you trying to do?
Yes, exporting audio in a lossy compressed format is slower than exporting as uncompressed PCM (such as WAV or AIFF).
The “Amplify” effect applies a specified amount of gain - that is, it amplifies “by” the specified amount.
To amplify “to” a specified level is called “peak level normalizing” (often shortened to simply “normalizing”) and is performed using the Normalization effect.
You can normalize multiple tracks to a specified peak level - that’s what peak level normalizing does.
Do you mean that you want to amplify multiple tracks in the same project so that the highest peak found in any of the tracks determines the amplification amount, and that amount of amplification is then applied to each track?
Where do “Chains” come into this?
Where does converting to AC3 come into this?
I am “normalising” my video collection because I am tired of some of them being so soft. They are all 5.1 channel. This means that I cannot use the Normalize effetc, I have to use Amplify, and set the maximum level to -0.3db.
Ideally I would like to be able to use File-> Apply Chain to automate the process. Unfortunately, when you create a Chain that applies Effect->Amplify, the parameter that it uses is Ratio - ie by how much should it amplify/attenuate. If you set Maximum Level to -0.3db, it has a look at the currently loaded file, works out the amplification ratio needed for that file and saves it. You cannot save a Maximum Level parameter. This means that you cannot automate using Apply Chains.
This then means that you have to Import the audio file, sit there for the 3 minutes it takes to open the AC3 file. Then use Effect Amplify and wait until it completes. Then you have to Export the modified file, and sit there for 6 - 8 minutes while it does that.
Nearly 15 minutes for movie. 
Audacity is an audio editor. How are you putting the processed audio back into the video file? Can’t your video software increase the audio level?
I rip the disks with MakeMKV. By far the easiest and quickest. Then use MKVCleaver to get the audio out (Audacity is too slow reading the audio in a MKV file). Process the audio, then replace the audio track with MKVMerge.
It may help to add a 2nd hard drive. i.e. Read from one drive and write to a different drive. That can sometimes cut the time in half (if the hard drive is the bottleneck) because the drive doesn’t have to switch back-and-forth between reading & writing, and the read/write head doesn’t have to jump-around between the read-file and the write file. That probaby means using the 2nd drive for Audacity’s temporary file, and reading the original from the 1st drive and writing the final file back to the 1st drive.
You might also try [u]TAudioConverter[/u] because it won’t have to make a temporary file (like an audio editor has to do) and it might read directly from the original audio/video file. It has a normalization “filter” (which I assume normalizes to 0dB).
You could also try a video editor. Most video editors have some basic audio editing capabilities built-in. I’ve used Corel Video Studio and Cyberlink Power Director, but I’ve never worked with MKV files.
I am “normalising” my video collection because I am tired of some of them being so soft. They are all 5.1 channel. This means that I cannot use the Normalize effetc, I have to use Amplify, and set the maximum level to -0.3db.
That’s intentional, There is a loudness standard for AC3 audio in movies. It’s not like the digital music Loudness War where everybody tries to be louder than everybody else.
This then means that you have to Import the audio file, sit there for the 3 minutes it takes to open the AC3 file. Then use Effect Amplify and wait until it completes. Then you have to Export the modified file, and sit there for 6 - 8 minutes while it does that.
Is that so terrible? Audio & video editing usually takes time…
I don’t know if it will help, but if the Audacity project rate bottom left is the not same rate as the tracks then the required resampling will slow down the export.
Gale
@ Gale Andrews Audacity automatically sets the project rate correctly.
@DVDdoug Yes, if they were all AC3 they would all be the same level (more or less), but then there are the DTS ones. I have tried TAudioConverter. Does the job perfectly - batch mode, normalise while extracting, set output path. All that is left is MKVMerge. That has to be done one by one, but I can do them as and when, it only takes 2 minutes.
So, TAudioConverter gets my thumbs up, thanks.