VSO released v2.1.14 ÃŸeta and those comments from the VSO Developpers:
Sound source (especially on MP3) is a real nightmare, as the source can go to barely understandable to incredibly loud.
It's not a problem in ConvertX in fact. The encoder can take the whole dynamic of AC-3, so if the source is very loud, it'll be encoded very loud. On our reference equipment it doesn't saturate or distord, but the problem is that most audio equipment is not able to support such a loudness, thus result in audio distorsion because of poor AC-3 decoder. Also Computer sound players often handle the situation simply by dividing the output signal by 2 - thus distorsion is not to be ear even if the source is massively loud.
And the sound compressor make things even worse in such case. That's why this setting is off by default.
There's not a lot of solution. I've added a detection of loud MP3 sources (only on MP3 so far), to limit the problem, but as long as the source will be too loud, the resulting AC-3 will be loud as well.
I set this bug as fixed, but I'm sure there will be other samples from other sources that may complain of being too loud...
Let us know how v2.1.214 works for you, just download it from the VSO Webpage, you will get the latest v2.1.214