I saw an option in LPAC "joint stereo". Could this option originate a different stereo image of the file, just like lossy codecs that use the joint stereo technique do?
No. LPAC is completely lossless.
From the Readme:
Joint Stereo:
Tries to make use of the dependencies between the two channels of a stereo signal, which leads to better compression if the audio file mainly contains components which lay in the center, e.g. dominant vocal parts. This feature is not available in Fast Compression mode. In other compression modes, it should always be enabled.
if your still not sure, just decode the lpac file and fc it ;-)
I'm not an expert, but as I understand it, it is extremely important for lossless compressor to use M-S matrixing in order to be efficient. Since there is usually a strong correlation between left and right channel, one way lossless audio compression can save some space is to find the delta of the two channel, which won't have as much amplitude as either left or right (less amplitude = less bits needed) the other channel being the addition of both, which won't be much more complex than either left or right... well, as we can see there's so much mileage to do before even aproaching what will be REAL compression. Compression that will take into account the extreme redundancy of all the notes played by one specefic instrument. The future of compression resides in something that will remind a midi file on steroids....