I got talking about this in another thread recently, and rather than take their discussion off-topic, I thought it best to start this new thread here.
According to the Wikipedia:
High Definition Compatible Digital, or HDCD is a patented encode-decode process, now owned by Microsoft, that improves the audio quality of standard Redbook audio CDs, while retaining backward compatibility with existing Compact disc players.
In other threads I've gone round and round with this HDCD thing ...
Yes, its currently still in production.
Yes, I am told new albums are coming out in with HDCD coding -
Yes, HDCD discs play fine in regular players, computers or DVD machines.
Yes, its invisible unless you have the Brown and Burr chips or their equivalent to decode it.
Yes, Harman seems to like it - my HK changer has it, the Oppo passes the signal through the optical connection and the HK AVR 7300 receiver can decode it (see image below).