HDCD - An Overview

High Definition Compatible Digital® (HDCD®) is a patented encode/decode process for delivering better audio quality on CDs. HDCD has been used in the recording of many thousands of CD titles, which include more than 250 Billboard Top 200 recordings and more than 175 GRAMMY® nominations, and account for well more than 300 million CDs sold. (As an example the following links are listings of 4 years of the HDCD Grammy nominees in 1998, 1999, 2000, and 2001)

As compared to conventional CD's, HDCD-encoded CDs can sound markedly superior for two reasons: First of all the superb sonic quality provided by the Pacific Microsonics A-D converters which still to this day are considered by many to be the finest sounding A-D converters ever made. And it should be noted here that the Pacific Microsonics A-D converters are the only A-D converters designed to encode HDCD. In addition HDCD-encoded CD's can also sound better because they are encoded with 20 bits of real musical information, as compared with 16 bits for all other CD's. From a theoretical technical perspective, at 6db of dynamic range per bit, a 20 bit recording has 24db more dynamic range than a 16 bit recording.

HDCD overcomes the limitation of the 16-bit CD format by using a sophisticated system to encode the additional 4 bits onto the CD while remaining completely compatible with the existing CD format. As they are 20-bit recordings, HDCD-encoded CD's can provide more dynamic range, a more focused 3-D soundstage, and noticeably more natural vocal and musical timbre. With an HDCD-encoded CD, you get more of the body, depth, and emotion of the original performancerather than what is more typical which is a flatter, more "digital" imitation.

When an engineer is using a Pacific Microsonics for analog-digital conversion there are also some minor HDCD-encoding options which can be utilized such as Low-Level Extension and Peak Extend. But in practice these options are seldom usedand even when utilized the resulting difference is subtle at best.

HDCD technology was originally developed by Keith Johnson and Pflash Pflaumer, two preeminent technologists in the audio arena. In 1996, they founded Pacific Microsonics, Inc. (PMI), a California-based audio technology licensing company, in order to improve the quality of digital audio recordings and playback while remaining compatible with established digital formats.

If you would like to hear how good HDCD can sound, Keith Johnson also does recordings for Reference Recordings and you can obtain any of their HDCD CD's directly from their if you wish.

For more info on HDCD click here and here.

You can also access a basic HDCD FAQ is here.

For some technical articles on HDCD here is a link. An article on HDCD mastering mixing, and recording is here. Another article on HDCD is .

To date there have been well over 5000 HDCD-encoded recordings released on CD. While the following lists are by no means complete or up to date, as there are more being released every year, here are some useful links of HDCD-encoded CD's which  you can explore:

Here is another listing of some HDCD CD's currently available. This listing is presumably, or at least hopefully, up-to-date and accurate:

HDCD and Pacific Microsonics A-D Converters

HDCD's are encoded using either the Pacific Microsonics Model One or Model Two. It just so happens that these are also the best sounding A-D converters ever made. Plus both the Model One, and especially the Model Two, contain a superb sounding D-A converter (which also happen to decode HDCD as might be expected). BTW you might be interested to know that somewhere between 2-3 million dollars was spent in the combined development of the Pacific Microsonics Model One and the subsequent Model Two. (The Model Two being an upgrade of the Model One). That is an enormous amount of money to spend developing an audio productbe it a professional or a high end audio component. Whereas the budget for the development of most professional or high end audio products is a mere fraction of that. The reason that so much money was poured into this project was that at the time, like Dolby, the business model for Pacific Microsonics was to license the HDCD-decoding process to CD Player and D-A manufacturers. And licensing 100's of millions of CD players and D-A converters would obviously produce a significant financial return on investment. So in essence the development of the Pacific Microsonics A-D converters was subsidized by this business model. (Furthermore without that subsidization they would never have even come into existence in the first place.) And because the idea was to be able to audibly demonstrate the sonic superiority of the HDCD process, the A-D (and D-A) designs were essentially price-no-object converters, designed and built to be as good as was humanly possible. This thus ensured that when HDCD-encoded recordings were demonstrated in a listening session (most especially to either to licensee manufacturers or key audio industry insiders) that, assuming the other aspects of the recording were well-done, the result was a superior sonic result as compared to conventional CD's which were not recorded with such stellar A-D converters and not HDCD-encoded with 20 bits.

Furthermore working at higher bit levels and/or higher sampling rates puts even more stringent requirements on accurate word clocking to ensure lowest possible jitter, etc. etc. All of this being necessaryas in order to make the HDCD encode/decode process work up to it's full potential everything in the digital chain had to be at the highest level possible from a technical point of view.

It would take an extensive white paper to thoroughly discuss all of the elements that went into designing and manufacturing the Pacific Microsonics A-D and D-A converters. But suffice it to say that by combining world-class audio engineers with what was in essence a virtually unlimited development budget and literally years of development timethat this was the combination that was required to produce the high level of sonic excellence produced by the Pacific Microsonics converters.

Euphonix Manufactures the Model Two

In September 2000, PMI was acquired by Microsoft for their intellectual property. At that point Euphonix was then licensed to continue manufacturing the Model Two and did so for a number of years until some critical parts were no longer available, at which point manufacturing of the Model Two ceased. Fortunately enough spare parts were stockpiled so that the existing Model One's and Model Two's could be serviced well into the future. In fact, still as of 2013, parts as well as the requisite expertise are still available if a repair should be required.

At the time, when the manufacturing of the Model Two was taken over by Euphonix, Alan Goodwin became concerned about whether or not the manufacturing quality was as good as when the converters were made by Pacific Microsonics themselves. So he took a trip to California to see for himself. First he went to the Euphonix factory and saw the manufacturing facility. What he learned was that essentially that the entire Pacific Microsonics factoryincluding all of the parts, test equipment, and key peoplehad been successfully transported and set-up intact in one corner of the much larger Euphonix facility. And that before shipping, that every single Model Two was then transported over to Keith Johnson, the key audio engineer most responsible for the design of the Model Two, for him to personally evaluate and sign-off on. Alan Goodwin then went to see Keith Johnson and was fortunate enough to have the opportunity to sit in on a Model Two listening comparison sessionthat being the final stage of the evaluation by Keith Johnson. This listening test utilized an analog master tape, which contained three different types of music selected to highlight a variety of potential sonic challenges. By comparing the direct sound of the master tape with that same feed run through the A-D and D-A converters in real-time, this test as set-up by Keith Johnson was quite a revealing one! The bottom line was that the sonic difference was very, very subtle thus proving the sonic excellence of the Model Two beyond a shadow of a doubt. After the testing session Keith Johnson stated that, from his hand-on testing of each unit produced at Euphonix, that not only had the quality of the Model Two been maintained but that they had actually been tweaked to be even a bit better both measurably and audibly!

However the unfortunate fact at this point is that the manufacturing of the Model Two has ceased due to some key parts being unobtainable. So the only way to obtain a Model One or Model Two is either rent one or to attempt to purchase one of the existing ones from someone who owns one. The only other alternative of course is to engage the services of one of the top recording or mastering engineers who are fortunate enough to have a Pacific Microsonics Model One or Model Two in their studio. There are even a number of studios have more than one so they can equip multiple rooms at their facilities.

HDCD Recordings for CD Players

The reason that HDCD's continue to be released is that the Model One's and Model Two's are still being used by a good number of the top echelon of recording and mastering engineers around the worldand so (as of 2013) many releases are still being encoded with HDCD to this day. Note that some encoded CD's may not have the HDCD logo on the CD jacket, however if the HDCD indicator lights up on your HDCD-equipped CD player then you know for sure that you are listening to HDCD being decoded.

HDCD Recordings for Music Servers

With regard to music servers, what music lovers are seeking first of all is music that they most enjoy listening to. If there is more than one version of that music available, say an older conventional CD with more primitive A-D conversion and mastering versus a better sounding recording, obviously the best choice is the best sounding version of that prized recording that is available. While there are a growing but still limited number of high resolution files availablesome of which are sonically superior to a CD or an HDCD-encoded CDthere is still a lot of music for which the best sounding digital version available is from an HDCD-encoded CD. That is why to this day HDCD CD's are still being sought out by music lovers who are in the know. As it is well-known now that, all things being equal, a 20-bit recording is superior to a 16-bit recording. And that, in theory at least and all things being equal, a digital recording made with a better A-D converter is a better sounding recording. And since as you know all HDCD recordings were done using a Model One or Model Two, even for that reason alone these recordings can be (but not necessarily will always be due to other aspects of how the recording was made) sonically superior.

Tip: If you have a music file from an HDCD-encoded CD on a music server plus a DAC which will decode HDCD, you will know if you are hearing HDCD being decoded if the HDCD light on the DAC comes on. In addition if when listening via a music server to a music file, one that you know for sure is HDCD-encoded, if you see the HDCD indicator light come on you know that you are getting a bit-for-bit signal into your DAC. So this becomes a very useful test to quickly and easily determine if your music server is properly set-up and operating correctly. As bit-for-bit accuracy is necessary in order to ensure top-level sonic performance from a music server in combination with a high quality outboard DAC.


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