Mike Moffat: Re-Creating the Musical Event Page 2

Harley: Your processors have a characteristic sound—apparently reflecting your sonic priorities. How does a designer translate to circuit design what he thinks the product should sound like?

Moffat: That's a complex question. For the tonal aspects, the [digital] filter's frequency-domain performance must be accurate. But there are other factors. The longer I stay in [digital processor design], the more I realize how much I don't know.

For example, if you have a lot of RF near the analog stages, the RF causes the analog stages to perform in a less than optimal manner. You take anybody's good preamp and load it up with RF—RF that may be only 20 to 30dB below the audio signal—and it will affect the sonic qualities of the preamp to a greater or lesser degree, depending on how well it's RF-protected. That gets to be complex in itself; the more you RF-protect something and roll it off, it can actually intrude into the treble presentation of the electronics. We try to keep the RF as low as possible. In the worst case—our least expensive product—we have in the high 60dB of RF rejection to 100MHz. Most digital audio products are only quoted on signal/noise ratio across the audioband.

The time-domain optimization is a very important part of getting the image right—hearing exactly where everything is. There are other factors as well. The grounding becomes much more critical in digital designs, particularly when they're mixed with analog designs, which of course occurs in every D/A converter. But the sonic goal is being tonally wonderful, wonderful from the standpoint of how it images, and quiet and free from noise and other spuriae.

The term "jitter" is overused. What's quoted primarily is a single figure generally measured in the picoseconds, and, in the poorer-performing units, nanoseconds. But what we're finding is that not only is the total amount of jitter important, but the frequency components of the jitter as well. Different jitter frequencies affect the sound in different ways.

I'm sure there are more things we'll find out about, but my thing is frequency-domain– and time-domain–optimized filters. You make it as quiet as possible and as jitter-free as possible. That translates to the best sound.

Harley: The sound of many products reflects their designers' sonic priorities. You, for example, seem to go for three-dimensionality and deep bass. How do a designer's sonic preferences end up in his product?

Moffat: My preferences emerge as various prototypes are developed. Again, I'm shooting for the same kind of rush I get listening to live music.

The goal has always been the Peter Walker thing—to re-create live music in the listening room. You learn things along the way, then refine other aspects of the design. When we learn how to do something, like bass—we learned how to do bass early on—we just keep on doing it and improve other aspects of the design.

I'm not trying to color it or take artistic license, I'm just trying to make it sound like the real thing. How you do that in the analog stages is to do analog circuits that are horrendously fast, particularly at the summing junction of the DAC. You try to keep it as fast as it can be and keep the distortion as low as possible. The analog stage [in a digital processor] is very different from the line stage you would use in a preamp. You have different priorities—settling time, glitch reduction—because the smaller the area under the curve of the glitches, the better it sounds.

Harley: Do you find much correlation between sound quality and measurements?

Moffat: Not all the time. If you rely on measurement only, you can design products than measure well but don't sound so good. If I improve a specification—and I'm talking about specifications other than the usual harmonic distortion and audioband S/N ratio—if I improve the RF S/N ratio to 100MHz, I know it's going to sound better. That's not a commonly measured specification. We're finding things to measure that aren't commonly measured. We've found empirically that, as you reduce the RF noise, you get nothing but better sound. As you reduce the settling time in the current-to-voltage converter and reduce the area under the curve in the glitching, you also get better sound.

Harley: Your latest project uses a laser-driven interface between transport and processor instead of a conventional LED-driven interface.

Moffat: The unit we brought [to the 1992 Summer CES] is an all-out design. The differences between that unit's interface and the AT&T—and the Toslink, for that matter—is that the AT&T and Toslink are LED-driven and ours is laser- driven. The AT&T interface is some 10 times faster than Toslink; the Toslink has about a 5MHz bandwidth and the AT&T has about a 50MHz bandwidth. The Toslink is way too slow.

As an experiment, we built a Gigahertz bandwidth device that was laser-driven. It was also "single mode," which means that if you look at it on a spectrum analyzer, you see one pip instead of a series of pips. Both the AT&T and the Toslink system are multi-mode. They work over a broad range of frequencies.

The laser system we developed involves some focusing and some critical distancing between parts. It has to be assembled in production to an accuracy of one to ten microns. We're now building an interface in the vicinity of 150MHz that is single-mode. The plan is to build a non–single-mode system with a Gigahertz bandwidth and determine which is really important—the single mode or the wide bandwidth. Then we'll take a look at what to offer as a product.

We will offer the all-out design. We're building a jig to assemble the thing to the tolerances required. We're also looking at offering a lower-cost, single-mode interface if that works out well. I'm optimistic.

Harley: So this is a practical system we're likely to see in Theta products in the near future?

Moffat: Oh, yes. Certainly by sometime in 1993.

Harley: Any idea what it will cost?

Moffat: The target on the 1GHz system—a complete system including the transmitter and fiber link, and a detector that would mount in a Generation III—is $1200 to $1500.

Harley: What do you hear when you widen the interface bandwidth?

Moffat: It's stunning. Layers of haze and veiling disappear, revealing nuances. Not just in a sense of more detail to the music, but there is more spatial information as well. When I first heard it my jaw hit the floor. I couldn't believe the differences it was making. It was a lot like the difference between a veiled and slow inexpensive preamplifier and a preamplifier that is faster and smoother at the same time and has a lot more detail. It's shocking.

Harley: That reminds me of something you said once said about moving a Toslink optical cable and hearing the images shift.

Moffat: I do that at dealer demos. I'll find whatever processor's hooked up optically, and get all the listeners there, and just take the cable and wind it around—curl it up—and then ask them to note where the images are. And I'll be sitting there holding the cable, and they'll notice where everything is, and then I let the cable go. When it springs back to its normal position, they say, "Wow, it really moved." It does.

Harley: Why do you think there is so little recognition of the sonic limitations of digital audio among professionals?

Moffat: Well, I think it's obvious that many of them don't give a shit as long as their CDs are selling. It's the people like us who care about good sound. We [audiophiles] have been given short shrift. Just look over the last 20 or 30 years. Going back to the 12AX7 [tube] we were talking about earlier: the 12AX7 was basically a commercial compromise to allow low-cost record players to be built. The kind of record player with an on/off switch—you turn it on, it starts spinning, you lift up the arm—had a 12AX7 in it. Companies are always going to be looking at cost.

Japan's a big market for Theta. They love our stuff, because it's an alternative to the stuff that was designed to perform as well as possible for as few dollars as possible. Actually, when you look at a Magnavox Bitstream player that you can buy for $200–$300, even at $300, that's a lot of electronics for the money. So the guy who's buying the average cheap system is getting a better deal.

Harley: Some would argue that differences in digital processors are academic—loudspeakers have a much greater effect on the reproduced sound.

Moffat: A friend of mine named John Koval believes that the only reason that any two speakers sound different is because they have different frequency responses. He will equalize one speaker to the other and then prove that no difference can be heard between the speakers. But I'll be over there and he'll be absolutely swearing that I can't tell them apart—but I know.

So one day, I took over an early prototype of the DS Pre. He said, "Okay, we're going to do a blind test." He's very emphatic about what he believes in. He hooks up the DS Pro and a cheap stock CD player through his A/B box that has relays and junk interconnects—throwaway cables that come with a $100 cassette player. He hooks it all up, gives me this little box, and I don't know which is which. I'm sitting there going back and forth. I was the only person in the room who picked out my processor ten out of ten times. After ten times he finally gave up.

But he couldn't hear the difference. Some people just don't hear the differences, but I have to think the reason they don't hear the differences is they don't want to hear the differences.

The guy who sells the exotic Vishay resistors came in [to Theta Digital]. He lives, talks, eats, and breathes resistors. He asked what we made. When we showed him, he asked what it did. We said, "It makes digital audio sound better." He said, "Well, digital audio's perfect, isn't it?" And we played it for him—compared a Generation II to a generic CD player—and he was just absolutely amazed. He left babbling.

Harley: One of your updates to a Theta processor was replacing the short piece of wire that carries the digital audio signal from the input jack to the pcb. Can a 3" piece of wire carrying digital audio make such a difference to the sound?

Moffat: The wire we use is very fast wire, made for the internal wiring harness in supercomputers. It's relatively expensive, but it's blindingly, screamingly fast. And since the first product we put it in—all the little wires to the jacks, and then on the larger units where we had the boards separated under different compartments—we use it for all the digital wiring between boards. It just sounds much better.

I don't want to sound like a nonscientific type, but I have to totally admit that that's just an empirical sort of decision which is normally not the way we do things here. Normally we try to have organized R&D programs. Because hopefully we're going to learn something about these things—other than vague generalities.


LarryMagoo's picture

Posting an interview more 25 years old????

Jim Austin's picture
Stereophile is gradually posting its archives online with the original publication date clearly indicated. You have a problem with that? Jim Austin, Editor Stereophile
supamark's picture

Is still quite relevant - he's one of the founders of Schiit Audio and is *still* innovating in the digital realm (their multibit DACs are the bee's knees in my opinion). And as one of the guys responsible for the outboard DAC as a product catagory he's kind of a big deal...

oh, and he's a great interview - check out his RMAF interview from 2018 along w/ his partner in Schiit Jason Stoddard on youtube. His statements about USB audio (vs S/PDIF) are both hilarious and accurate.

mpbrog61's picture

Thanks for interesting article. That's some good Schiit!

shadowplay0's picture

glad SOMEBODY get it

Herb Reichert's picture

to me,
every one of Moffet's comments
is a still-relevant grain of truth
just sayin'

Bogolu Haranath's picture

May be HR could review the Audiolab 6000A integrated-amp? ........ Hi-Fi news favorably reviewed the 6000A, recently ......... Amazon sells Audiolab 6000A for $900 :-) ..........

supamark's picture

Have you heard his thoughts on USB? they made me go and listen to USB vs S/PDIF and I discovered why there's all those USB fixer-upper gadgets (and now use S/PDIF whenever possible). Y'all need to get Mr. Moffat and Mr. Stoddard in for an interview, they're great together - comedy + knowledge = great interview to me.