Anyone who collects or has looked at Japanese papersleeve mini LP CD's will know that the companies who manufacture them like to offer distinctive mastering and disc types. Many see this as purely a gimmick to make the consumer buy the same album over and over, thinking they are going to get something which sounds better than what they bought before. We have seen different formats like SHM, HQCD and Blu-spec bandied about. I have read plenty of postings on many forums negating these formats, basically saying there is no difference in the sound compared to a standard manufactured CD.
However I recently came across a thread in the Computer Audiophile forum concerning this very subject and was amazed to read those posted by Barry Diament, who is a very highly regarded mastering engineer (he mastered the original CD issues of Yes and Led Zeppelin titles). He, quite emphatically stated that there is an audible difference between standard CD playback and the same mastering on an SHM disc. He says the SHM disc sounds more like the original master than the normal CD. What's more, when he ripped both discs to computer, the digital files sounded the same, both sounding similar to the master. So, by removing the digital files from the physical CD it sounded better! I take it the conclusion is that the manufacture of the CD somehow degrades the playback of the digital music, whereas the improvement of the SHM disc does not. According to Barry's experience, he has even noticed difference in CD's from different pressing plants. So it's not all just 1's and 0's. The physical medium does make a difference.
Below is a link to the Computer Audiophile thread and also to an article from the What Hi-fi web site which heard similar improvements from these discs.