o.k anybody know anything about shm-cd they claim there indistinguishable from the master?

If you talk to people who compare the sound of every different release of various CDs trying to find the best (you’ll find them on the Steve Hoffman Music Forums), what matters is the the tape or the file used and the mastering.

CD releases from different countries released at the same time can be different, and CD releases from the same country released at different times can be different. For example, the 2012 American reissue of album XXXX may have used the original master tape while the 2014 Japanese reissue may have used a safety copy, or vice versa. And then there’s the mastering. Who did it? Was it a good example of his work, did he hit this one out of the park, or did the record label force him to compress it? And on and on...

Of course, the most popular albums have had the most releases or reissues and are more likely to have some good and some bad releases. Some albums only have bad releases.

Some people just love SHM CDs too. I think the packaging is usually better quality at least. Sometimes an SHM CD is one of the best sounding, sometimes not.

Anyway the Hoffman Forum is the place to learn about these things, but remember that the differences between CDs that are significant to some people there may not be as significant to you, and there may not be a consensus as to which release is the best.

Also, every different release does not have a different mastering.  So many different releases, even from different countries, can have the same mastering.

One of the ’advantages’ of digital is you can make copies of the master without any sonic loss. So the big sonic differences that existed between various vinyl pressings from different countries is mostly a thing of the past. So if the sonic quality of the master is any good, all cd pressings made from that master will probably sound good as well.

The one remaining variable is the manufacturing process of the disc itself. In my experience Japanese cd pressings usually sound a little better, even if they use the same digital master as its source. I suspect this can be attributed to better manufacturing, as Japanese cd’s are much better centered than cd’s manufactured elsewhere. It seems the laser/transport has more difficulty reading discs which are not centered, causing errors that need to be corrected in the digital domain. This manipulation may affect sound quality.

SHM is only about the material of the disc, not about manufacturing or digital processing (like Victor’s K2 or XRCD mastering). The SHM cd’s do feel somewhat heavier than regular discs, but it seems a stretch to attribute any sonic benefits to this.

So the data is encoded as a series of on and off, or ones and zeros. This is the digital system, it's an encoded language. The actually transfer and storage of the data exists in the analogue world. A  flip flop is an electrical circuit, used to store a value, this is what the digital data is stored in with RAM.

The quality of the storage system/device and the retrieval of the data is all done in the analogue world. For example it could be via a cable, where the electrical signal energizes and de-energizes delivering the pattern representing the values of the data being conveyed. The device creating the analogue signal, electrically, through an oscillating stream of light, or a radio signal, what have you, the connecting medium through which the signal travels and the end device that through engineering has to read or discern what the signal represents have varying degrees of efficiency.

The encoding is called digital, as for the entire rest of the computing system including the transfer of the language it's electronics and can be transferred by light pulses or an electrical system, radio signals. All of these methods of transfer of a language are prone to mechanical limitations and failure.

Digital being the organized structure of the data may be perfect, the storage, retrieval and conversion from and back to the analogue world is not perfect. That is why the technology for storage, retrieval, computation and conversion is always being improved upon by engineering methods.

As for SHM CD this appears useful >

https://www.cdjapan.co.jp/feature/shmcd_allabout