Interviews

Pflaumer: That's true. In the human ear, the cochlea has hair cells that respond to about 80kHz. And yet, for steady-state sinewaves, even a young person can hear only 20kHz as a steady-state tone. As we get older, that deteriorates. But the sense of frequency extension is largely based on transient events—things that happen only in short instants of time.

The shape of a wavefront generates harmonics in the bone structure of the middle ear, which are then picked up by the hair cells in the cochlea and used to reconstruct the picture of that wavefront.

The army did quite a lot of research on perception of this kind of supersonic wavefront. It has a lot to do with spatial perception. The army wanted to understand how the location of gunshots can be pinpointed by listening. If you disturb the shape of the wavefront going into the ear, you very greatly disturb the ability to pinpoint the source of the sound. A lot of what we do is pay attention to these transients, which are very brief instants of time as opposed to steady-state high-frequency response. It turns out that the transient information is much more important than frequency extension.

Harley: I've noticed with HDCD an ultra-fine resolution of image placement in the soundstage.

Ritter: Yes, that's exactly right.

Harley: Can you describe in more detail how this transient information is reconstructed on playback?

Ritter: You can see why we're sort of closed-mouthed about these things. People don't know about this stuff. It's just one of the things that makes HDCD work. We don't want to give away some of this information.

Pflaumer: After the professional encoder is out there, if someone seriously wants to reverse-engineer it, they probably will. At that point, it's appropriate for us to do a full-blown AES technical paper on everything that's going on (footnote 5). But we're trying not to give the competition any head start at this point. We worked real hard for this information.

Harley: Going back to the hidden control code: the fact that you use the LSB only briefly avoids the problem of the control code being correlated with the music, which would tend to make it audible when played back undecoded.

Pflaumer: The encrypted channel uses spread-spectrum–like techniques. Even though the information that's in there might have distinct patterns, it's randomized. By the time the encrypted channel is actually inserted in the LSB, it has as close to random characteristics as you can get.

Harley: Is there any chance that the encrypted data could create problems for some D/A converters?

Pflaumer: No.

Harley: What's the availability of the HDCD decoder chip? If I were a digital-processor manufacturer and wanted a thousand pieces, when could you deliver?

Ritter: We are in full commercial production. You could get a thousand pieces in mid-February 1995. We have more than 17 licensees.

Harley: Tell me more about the algorithms that examine the high-resolution digital signal to determine what information to put in the encrypted control channel.

Pflaumer: Keith and I together formulated the original algorithms in very broad terms. As Keith mentioned, some of them were implemented as analog models—pieces of the algorithm, very early on, which Keith did. I'm responsible for taking all of those and turning them into digital algorithms and writing the DSP code to implement them. I've been working on this full-time since the beginning of 1990.

All of the DSP code is done in assembly language because it's all very time-critical. The prototype encoder had 11 Motorola 56001 DSP chips, and the algorithm was shoehorned into those 11 processors on the encode side. Everything was done in assembly code because the higher-level DSP compilers are too wasteful of cycles. The professional encoder will use the new Motorola 56007 processor running at 66MHz.

I also did the algorithm that is incorporated in the decoder chip, the PMD100. We had a consultant do the actual schematic design of the chip, but I did a mathematical specification, bit for bit, of what the chip should do in mathematical terms. Then I implemented that on the DSP engine, and we used that to generate the production test vectors for the silicon, and for the simulations before the silicon. The DSP implementation allowed us to hear playback precisely, bit for bit, through our part, long before we even had schematic diagrams of the chip, much less actual silicon. So we knew what it was going to sound like long before the chip actually existed. Nothing was left to chance.

Harley: Is it possible to make improvements in the encoding algorithm, yet keep the same decoder? If you get a large base of installed decoders, will they benefit from future improvements, or are the encoding algorithms fixed?

Pflaumer: Anything is possible. We are at this point pretty satisfied with the encoding. As we make improvements in our own D/A conversion, we hear more and more things in recordings that we've already made.

It's somewhat analogous to the situation with LPs. There are many great LPs, but nobody could actually hear everything that was there when they were made. It's only at the tail end of the life of LP playback equipment that it has reached the limit. People are still surprised at how much information is there.

This is not the case with most conventional CDs. The size of the information stream is so limiting that the better of the CD playback equipment reaches a certain threshold of performance. When you get to a perfect conversion of 16-bit CDs, then there isn't anything more you can do. We put in enough additional information that the D/A converters have not quite caught up yet.

Ritter: We're challenging conversion technology, particularly on the D/A side. As good as HDCD discs sound decoded today, they're going to sound even better three or four years from now.

Pflaumer: We're definitely upping the ante for all of high-end audio. Now there's a signal source with a resolution that requires doing everything right in order to hear that resolution. It's amazing how much is there. It surprised us.

Harley: The professional encoder used to make HDCD-encoded recordings is a critical element in the commercial acceptance of HDCD. When will it be available?

Ritter: We're looking to begin shipping pro encoders in June. We'll have parts of it working before that. Some of the earlier versions of it may go to a few very interested parties who are champing at the bit, and who are in very powerful positions in the industry.

The pro encoder is the entire thrust of the development effort at Pacific Microsonics today. We hired a significant full-time staff. We brought in René Jaeger, who has spent much of his career bringing state-of-the-art digital audio products to the recording industry [at Lexicon and other firms].

The level of accuracy and of distortion that the professional encoder is designed to achieve has never been done before in a digital audio recording product. We even developed our own discrete hybrid op-amp modules after investigating everything that was commercially available. We looked at the most expensive commercial monolithic op-amp parts and found them wanting.

We're not compromising on this as a product. It's going to be a product that will set the standard for—I was going to say digital audio recording. I'm going to say any audio recording. When this becomes available, I think it's going to set a new standard for the kind of quality that can be achieved in studio recording. To achieve that level of performance is quite a project. But we have the best possible people working on it, and we're quite far along in the development of it.

We have a number of encoders already sold to some of the top facilities in the recording industry. One of the largest mastering houses in the country, Georgetown Masters in Nashville, has ordered a half a dozen of them. A number of other people that I probably can't mention by name have ordered encoders—and these are very highly placed people in the recording industry. The fact that we're having such a high level of appreciation and establishment at that level bodes very well. This product has so much quality to it that once we get units to people that are doing classical recordings—and not just the esoteric labels, but the name labels—and they hear what this can do, we're quite confident that it's going to be recognized as a breakthrough. The more challenging the material, the more apparent the superiority.

Harley: What are the prospects for HDCD encoding on major labels?

Pflaumer: One of the surprising things to a lot of the recording engineers who have heard HDCD in a real studio environment is how neutral we are. They spent a lot of time getting a particular sound in a mix. When you take that final two-channel mix and record it on our encoder, then play it back, you get back what you put in. This is a tremendous surprise, because it's not true with any other A/D converter currently in use in the pro industry.

We were at a major recording studio in Los Angeles—I probably shouldn't say who—and other engineers who weren't involved in our project kept wandering in and listening. In many cases they couldn't tell which was the HDCD playback and which was the feed out of the board from the multitrack machines. You couldn't tell which was which. They'd never experienced that before with any kind of recorder.

We did some simultaneous tests with 30ips analog recordings. The analog sounded very, very good, but it had a character to it which told you it was an analog recording after final mix. And we did the same thing with good-quality studio A/D and D/A conversion. I don't want to mention names here, but the difference was dramatic.

People hear it and say, "When do I get mine?" "How do I get one?" "Am I in line?"

Harley: Do you see mainstream releases being HDCD-encoded from mastering engineers making the process available to individual artists, or record companies adopting HDCD wholesale?

Ritter: I think both mechanisms are going to occur. There's a third mechanism as well. There are a number of artists who will insist on HDCD before they get to the mastering facility. They'll insist upon it not necessarily because they're audiophiles, but because they want to preserve the quality of the music they've spent hundreds of hours creating. Listening to the output of the multitrack machine from the console, they get a presence, a vividness, and a palpability to the sound that are destroyed when they make the two-track digital master. The life and presence are taken out of the recording; the impact, the emotion, is gone.

But the artists and producers are very tuned-in to those things. They know that it motivates people to buy recordings. They see HDCD not only from an aesthetic point of view, but from a commercial point of view. Mastering facilities will demonstrate and recommend HDCD, artists are going to demand it, and it's possible that record companies will adopt it.

Johnson: One performer brought his master tapes here that had guitar solos. You think, okay, a guitar solo is a guitar solo. The guy is wailing into the amplifier, and the thing is about to blow its gourd from distortion. You think that a digital system isn't going to mess that up because it's already so distorted. How can anything more happen to it?

But in the hands of a very fine artist, that distortion has a real meaning. You can get into it. There's a very complicated tapestry of sound going on, and the guy's a master at weaving and controlling it. When that sound goes through a digital process that isn't right, the distortion is so horrible that you can't stand to be in the room. The musical intent is lost. It's not just the intent—there's nothing there.

I was shocked the first time I was exposed to this. I always thought that the studio people were going to have some problems using something as good as our encoder because a lot of their equipment has problems. It's been like using a Brownie camera. You spent $50,000 making a recording, and then you pass it through this little $24.95 A/D part. You can crank through hundreds of rolls of film, as it were, and 50 years from now that film is not going to be worth very much, as opposed to something that does it right and comes back the way it went in.

Pflaumer: For the first time, we let them get back in the final, distributed playback medium exactly what they put in. They don't have to mix by listening through the imperfect chain and trying to compensate for what's wrong with it.

Ritter: It's been wonderful for us to use Reference Recordings releases, but what you're hearing is not only HDCD, but Keith's recording technique and his whole approach. When you start getting commercial HDCD discs, they're not going to sound like Reference Recordings. Some of them will sound excellent, but they'll all sound different.

For example, some of the transfers we've already done using old analog master tapes are very simple recordings. You could almost say they were crude. But when you listen to the analog master, there's a sense of people in a room doing something. And that's preserved through HDCD.

When you went through a conventional digital transfer, the warts remained and the musical stuff got trashed. All you really had was a compendium of digital artifacts and the warts and errors of the recording. It's a very interesting thing to hear.

The point is that HDCD is neutral. HDCD recordings don't sound like Keith Johnson recordings, as wonderful as those are. They sound like whatever you put into it. You're going to start seeing a whole spectrum of different kinds of sounds coming out of HDCD once the encoders get out there.

Harley: A limitation, though, is that any signal that has ever been digitized with 16-bit linear encoding won't benefit from HDCD.

Ritter: Yes. If you have a 20-bit master, we can preserve the dynamic-range information. But you're stuck with the distortion and the frequency-extension limitations.

Johnson: Then there's not much you can do. The information is already lost.

Harley: Are you worried about the "not invented here" syndrome creating resistance to HDCD in the industry?

Ritter: Even though Dolby noise reduction wasn't invented by any large electronics company, it became ubiquitous in the marketplace because it works. Because people who buy the products demanded it, the electronics companies really had no choice.

And Ray Dolby was reasonable in how he did business with those companies. He gave them a situation where he got a small royalty out of a large market, and did quite well. It wasn't painful for them to do business with Dolby—and we'll be the same way.

We think that any company, even a very large company, that takes a clear-eyed look at the bottom-line impact of using HDCD technology will recognize that their products will sound better and they'll make money from it. For all those reasons, we think HDCD could migrate essentially to every area of the market. In fact, there's no reason why it can't become a standard.

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Footnote 5: See www.aes.org/e-lib/browse.cfm?elib=7387.—John Atkinson