hi, until now I used ML 2.3 and I set my audio levels in Canon's default menu, in newer nightly build I have 3 options to set audio levels: analog gain, mic boost & digital gain. Which should I use to make the same effect as in Canon's menu. I also noticed that analog gain has much more background noise than mic boost, also I need to pump up mic boost to +30dB to even hear something. I'm using Rode Videomic.
I dont know the answer to your question since I dont use the audio on my 600d. You or may not find the answer here.
http://www.magiclantern.fm/forum/index.php?topic=2032.0
There may be a better thread in here to answer that question. Searching is not the greatest on this site but I am pretty sure that has been discussed previously. If you cant find the answer then start tweaking the settings and find the goodness.