In our continuing story of the creation of the Digital Lens we're finally at the point where we have a roadmap of what we want to build. Now it is time to actually build it.
This is the point, as the old saying goes, where the rubber meets the road. And what's interesting about this juncture is the number of times developers arrive here only to discover that their beautiful idea wasn't worth the gamble – and the new circuit that doesn't live up to expectations. Throughout audio history, as in every field, there are more failures than successes (and you only hear about the successes). But, these are paths that must be taken if we are going to change the landscape.
This point in history was about 30 years ago and, back then, digital audio was somewhat like the Wild West. No one knew what was and wasn't going to be sonically important: green pens, degaussers, clamps, cables, and new technologies. What mattered is that we tried new directions and then auditioned the results.
Most of what was being tried were either tweaks or additions/modifications to existing products. I was venturing out into the wild with a new and never-tried-before category of product. A standalone digital in and out separate. Today, upsamplers, isolators, re-clockers, and interfaces are common. Back then, this was new and uncharted territory.
The PS Audio Digital Lens.
As an analog designer I understand how digital audio works but have zero experience building anything. I needed someone that not only understood digital audio but could grasp the technical challenges ahead and figure out how to mechanize the whole apparatus.
Enter, Bob Stadtherr. Bob, who has been PS Audio's chief engineer for the past 30 years, was then working as the head engineer at a theater lighting company in San Luis Obispo, California. I had hired him from afar because he was rumored to be a good engineer who could pretty easily design and program our front panel displays for the Genesis servo amplifiers.
At the time, I had been relying upon another outside engineer who had been working on our front panel display for an agonizing six months and still he couldn't deliver a finished product to us. He was stuck on the programming of the display interface. Out of frustration, I fired that guy and took a shot with Bob, who took one look at the schematic of the display and asked, "what was this guy smoking?"
Oy. Bob wanted to scrap six months of work and start fresh. Reluctantly, I agreed. Two weeks later Bob delivered a fully-functioning front panel display. I was frankly stunned. When asked what programming language he used, I was told, none. He wrote the entire program in assembly (this is the actual bit-for-bit machine language used at the silicon level and is the most efficient but challenging way of programming).
Bob had my attention.
And he had done this in his spare time.
Just for your reference, 1993, when all of this was happening, saw the introduction of a new idea. It was called the World Wide Web. Yup. 1993 saw the launch of the world's first web browser and, for the few that had access through noisy telephone modems, a new world of WWW was about to open. There was no such thing in my world like e-mail or browsing for answers.
We were on our own.
Past attempts at explaining my idea of a standalone separate that would connect to a CD player, take a gulp of its digital output, fill a "water tank" full of those digital bits, and then parse out the perfect results with a fixed low-jitter clock into an output wave shaper saw a lot of head scratching and requests for more detailed information which, as an analog designer, I could not provide.
One 15-minute phone conversation with Bob and he repeated the entire concept back to me with such clarity as to make me drop the phone. Not only did he grasp the concept but in the next 10 minutes he began explaining to me the pitfalls we would be facing.
I had the right guy.
My simplistic view of filling up a digital "water tank" and then, at some later time, outputting the tank's contents through a fixed output clock had what felt like a fatal flaw. Turns out the data and the clock coming out of a CD player is variable – unpredictable. The reason for this is simple: the laser mechanism that is reading the digital data might struggle reading some parts of the CD, while flying through other parts. Plus, the speed of the CD's rotation is variable too. Like a vinyl record, it takes less/more time to read depending on where in the disk you are – closer or farther from the center of the disc.
At this point in the story, it's instructive to remember the basic problem we're trying to solve. The CD player provides the master clock that is running your DAC. Because that clock is not only variable, but pays zero attention to jitter and noise, it's a horrible impediment to great sound. The Mark Levinson DAC I had mentioned in an earlier installment gave lip service to this problem by adding a small "water tank" memory buffer at the input of their product, but its output used a means of varying faster and slower the data rate at its output too. And now, once Bob explained why they did that, it became clear we had a major problem mechanizing my idea of the fixed low-jitter clock.
(The reason a fixed clock was needed was for the goal of eliminating jitter. A variable clock is always going to have high levels of jitter. Only a fixed-frequency clock can really provide the perfect low jitter output we wanted. Today, there are relatively low-jitter variable clocks available, but there the trick is to slow down the variability to a frequency below human hearing, like maybe 1 or 2 seconds. This is what our engineer Ted Smith does in our DirectStream technology, which came 30 years later. But, back then…)
Bob went away to think about the problem and, within a week, came back with the answer.
The intelligent buffer.
Bob had come up with a fascinating idea that would potentially solve our big hurdle. He called it the Intelligent Buffer.
The problems were the variable speed at which a CD or DVD player delivers data, and the system's master clock. Sometimes the data and clock came out quickly; other times they would slow down as the laser mechanism tried to read a scratched or dirty part of a CD.
Bob's idea for this buffer was relatively "simple." Because the CD player provided both the musical data and the master clock (this clock tells us how much data to expect and at what speed) Bob would read the master clock's frequency and then adjust the length of the buffer to accommodate the expected data. And here's the trick. We don't want this buffer (our water tank) to run out of data or to get so full it can't accept more. If we run out of data, then we get a pause in the music. If we overrun the data and it chokes, we get a tick or blip in the music.
Because we are using a fixed-frequency output clock, a simple on-the-fly math calculation can set the difference between the incoming master clock frequency and the output fixed frequency of our fancy low-jitter clock. Thus, the buffer's length changes on the fly (“intelligently”) to make sure we never run out of data, and never get too much to clog the system.
The only downside is a phenomena we call latency. The signal is delayed from real time playback, something that matters if you're watching a movie or trying to synch a person's lips with their speech, but hey! This was an audiophile device designed for music. Screw the video guys.
It took Bob two months to design, build, test, and deliver to us a working Digital Lens.
And at this juncture, it is again instructive to recall that we didn't yet know if this whole exercise would be worth it. What if, after all this trouble and ingenuity we would put it in the system and get meh results? Honestly, given that we could hear differences in the CD/DAC systems of the day by coloring a CD's edge with a green pen, I wasn't too worried about hearing improvements.
My partner Arnie Nudell and I listened to the first Digital Lens and were absolutely stunned. Not only did it make an improvement, it took the digital audio experience to a place we had only dreamed about. The increased openness, depth, and spaciousness we heard on that day recalibrated everything we had ever imagined possible. Suddenly, our vinyl had been bested in ways we never dreamt about.
Over the years, the Digital Lens became a standard-bearer for standalone digital interfaces. Even today, if you find one on eBay, it is swooped up instantly.
Lastly, every digital product we have made at PS Audio in the ensuing 30 years and up until today has a version of this exact intelligent buffer/fixed output clock and wave shaper built into our digital products.
And its inventor, Bob Stadtherr, is still cranking out beautifully-designed innovative products to this day.
Go Bob!
