Digital Drive

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RE: Thanks for the Clarity on HDCD - Charles post is a must read

Posted by Charles Hansen on June 13, 2017 at 20:41:14:
>> I still see HDCD show up on Grateful Dead releases. My guess is they like the AD processor. <<

When it was first released the Pacific Microsonics A/D was dramatically better than the then-ubiquitous Sony - which is unsurprising as not many audiophiles have Sony preamps in their systems. IMO, the PM converters are still one of the top three or four in the world from the standpoint of sonic performance. Keith Johnson is an excellent designer and knows how to make a good sounding piece of equipment. (Think of Keith's other designs for Spectral Audio, for example.)

>> I know there are HDCD lists out there, do any of them show whether the processing was actually used? <<

It is true that there are many "HDCD lists" out on the interwebs. The problem is that the PM A/D converter will light up the "HDCD" light on *any* disc made using it - even if the mastering engineer turned all of the HDCD encoding features off. This is even true for all Reference Recording (Keith Johnson's label) releases after 2009 - they continued to use the PM A/D converter as it sounds very good, but with all the HDCD features turned off as there is almost no way to decode it any more.

The way the world was able to "peek behind the curtain" was when Foobar released their HDCD decoding add-on module. If you are curious just download Foobar for free and click on the link below for commands you can cut-and-paste that will display which HDCD features are actually engaged on any particular disc.

>> Were the PM chips in the DACs as good as the AD processors? <<

In the last millennium, only three high-end manufacturers had the knowledge to build custom digital filters - Wadia, Theta, and almost a decade later, dCS. All other manufacturers used off-the-shelf chips. Of those chips, the Pacific Microsonics combination digital filter/HDCD decoder had a good reputation for sonics for several years. Its digital filter was a conventional brickwall design, but had perhaps 1.5x or 2x more taps than other brands. The problem was that it did not support sample rates above 48kHz. So for about 5 years, the PMD-100 was the "go-to" digital filter chip for high-end manufacturers and even a couple of mid-fi brands - but *never* the mass market. The PMD-100 digital filter only cost about $5 more than a non-HDCD part, but also required the manufacturer to pony up a $5,000 licensing fee, which was later raised to $10,000.

Once true high-resolution became available in the form of DVD in 1997, high-end manufacturers had to choose between high-res and HDCD decoding. I think that maybe one or two products were made (briefly) with two digital filters in order to support both. Finally PM released the PMD-200, which was a pre-programmed Motorola DSP chip that could both decode HDCD and also provide digital filtering for high sample rates. As far as I can tell Motorola only made a sample batch of these parts. They showed up in the Sonic Frontiers DACs for a short time, and then Microsoft purchased HDCD lock, stock, and barrel. For several years in the early 2000s, Windows Media Player would decode HDCD, but I don't know that anybody cared or even really noticed.

By the time that HDCD had died, almost all DAC chips came with their own built-in digital filters. A few had selectable algorithms, but just as with IC op-amps, I don't think that there are people at large semiconductor manufacturing companies sitting around doing listening tests to make the very best sounding filters (or op-amps).

"If you want it done right, do it yourself" is an interesting saying and there are now at least a dozen high-end companies creating their own digital filters. It seems clear that the only reason to do this would be if you really believed it sounded better than what was available off-the-shelf in a DAC chip (although I'm sure there are cynics who will say it all sounds the same and is just an excuse to charge more).

As always, strictly my own opinions and not necessarily those of my employer or Mother Theresa.