November 2017 has been a tough month for the audio industry: we lost some of the greats in our little world. Arnie Nudell of Infinity fame, Dick Shahinian of Shahinian Acoustics Ltd, and Charley Hansen of Ayre all passed away this month. I knew both Dick Shahinian and Charley Hansen personally, and all three were the kind of writ-large personality that makes a deep impression, and that creates a deep chasm when they are lost to us.
In 2015, we spoke to Charley Hansen as part of our Digital Buyers Guide, and we think it's a fitting tribute to the man to read his own words rather than more platitudes. I think he'd have liked that.
Hi-Fi+ Talks with Visionary Digital Audio Equipment Designers
Interview with Charles Hansen of Ayre Acoustics
Hi-Fi+: How did you become interested in digital audio design?
Charles Hansen: There were two driving forces. The first was when the LP was still "king of the world", in the late 1980s. This was an era of superbly innovative designs on the playback side, with things like Bill Firebaugh's zero-clearance turntable spindle bearing, John Bicht's air-bearing tonearm, and a completely new level of performance from moving-coil phono cartridges using new advanced material technologies. Times were exciting, and great advances were being made.
I was interested in a no-compromise approach to the full analog record/replay chain and wanted to understand the full possibilities of creating an incredible musical experience, which clearly analog can do. I began to explore, and was a bit taken aback to find fundamental limitations that had no practical solutions that I could see.
As examples of these limitations, the cutterheads used to make an LP acetate have huge resonances in the top octave that are controlled (but not cured) by applying massive amounts of feedback from an incredibly powerful amplifier (hundreds of watts). The basic geometry of the playback stylus motion is not well defined due to the practical limitations of the elastomer (e.g., rubber) ‘bearing’ that allow the cantilever to move in unwanted ways. These are just two examples, and there are many more, both in LP and magnetic tape.
The second was the realization that early digital audio was not well developed at all. Everybody familiar with high performance analog could easily hear that digital had real problems. The general thinking then was that the CD standard simply set both the sampling rate and bit depth too low. When the DVD spec was finalized in late 1996, Pioneer was pivotal in having 96/24 capability included. That was really the trigger point for me. It seemed that if some of the fundamental limitations of analog could be bypassed, a truly high level of performance could be achieved.
Everybody loves the convenience that digital provides, along with the capability to have perfect copies of a digital master recording. It was obvious that digital would become the dominant method of music playback. Yet digital audio at that time simply didn't nourish the soul.
That is how I became interested in digital audio design. Was it possible to equal, or even surpass, the best analog reproduction with digital technology? I love challenges and this was a good one.
Hi-Fi+: When you are developing top-tier digital audio products, which performance parameters do you think have the greatest overall impact on sound quality?
CH: A real problem is that there are almost no measurable parameters that correlate with perceived sound quality, or even more importantly, on how well the musical experience is communicated to us. This is true for both digital and analog technologies. Given that, I would say that time-related performance is the most critical aspect of sound reproduction in general, and digital is no exception. There is far more to this than just using high sampling rates or a certain digital filter. And there is the issue of feedback and how it is used — preferably not at all.
When I look back at everything I've done, from loudspeakers to analog and digital electronics, I think that there is an underlying thread related to time — both timing issues and the time domain in general. The ear/brain is far more sensitive to time-related information than any other parameter.
Transducer diaphragms (both microphones and loudspeakers) have significant energy storage problems. They ‘break up’ and release energy in a way that smears the time information, just as a cymbal smears the energy impulse of the stick impact, or a guitar smears the energy impulse of the pick attack. Most loudspeakers claim to be ‘reproducers’, but in actuality are actually ‘producers’ (much as musical instruments are) to one degree or another, even most current designs.
In analog circuitry, feedback loops take the time-delayed signal from the output and send it back to the input in an attempt to correct an error that has already occurred. This creates a form of time distortion that cannot currently be measured, yet is clearly audible. The math (and test equipment) tells us that the correction happens quickly enough, but our ears tell us something quite different.
There have been many amplifiers made with adjustable levels of feedback, and changing it changes the sound in obvious ways. Which is correct? I've found the answer to be simple. If feedback is good, use as much as possible — if it's not good, then don't use any. The products that have used very high levels of feedback (yielding incredible measurements) have not stood the test of time and are no longer made. In contrast, more and more designers are copying Ayre’s zero-feedback approach. We've never done anything else and we have over two decades of experience in this area.
In digital systems we have the twin errors of insufficient time resolution from a low sampling rate, combined with the energy smear created by the filters required to meet sampling theory requirements. (Analog and digital filters are no different in this regard — there are no free lunches.)
The fact that the filter-less ‘non-oversampling’ D/A converters (which don't even try to comply with sampling theory) can sound musical provides irrefutable evidence that our understanding of what is truly important to the human ear/brain is currently incomplete.
Hi-Fi+: In simple terms, what do you feel sets your designs and products apart from most other ones the market?
CH: My background is in physics, where things are looked at from the level of fundamental principles. This provides a different perspective than a conventional education in engineering.
The difficulty with engineering education is that its vision can be limiting. An engineer experienced in analog design finds many digital concepts to be non-intuitive, abstract, and impenetrable. It took many years for the traditional high-performance analog audio companies to even dip their toes in the complex waters of digital. Many of their early products showed promise, but did not fulfill the potential of digital.
Digital engineers, who tend to approach things from the abstraction that digital theory provides, design nearly all digital audio products. Yet if digital audio actually worked according to theory, then the game would have ended with the introduction of the CD in 1982 – ‘perfect sound forever’. In the real world there are no such things as ones and zeroes traveling down wires. Instead there are electrical fields in the conductors that create analog voltage levels, which are interpreted as ones and zeroes at imperfectly defined times.
Suddenly there is a lot of room for mischief. All of the limitations of digital audio are actually analog limitations. There are no infinitely steep waveform edges. There is no clock signal that is perfectly uniform, either in time or amplitude. There are no perfect converters between the two domains, yet all audio signals both start and end in the analog domain. The list goes on and on.
In addition all digital audio products have analog audio circuitry as well. Few digital engineers are aware of the subtleties hiding in analog design, where things like the bias level of each stage in the circuit makes a sonic difference. Many just resort to using pre-packaged IC op-amps, as they have as little understanding of analog design. Ayre's digital audio products are rooted in a deep understanding of both domains. Only by knowing the limitations and their causes can we find ways to surmount them.
Hi-Fi+: What do you consider your top one or two product digital audio design achievements thus far? What makes those products special from your point of view?
CH: Ayre's first digital product was the D-1 DVD/CD player from 1999. It was one of the very first high-resolution digital players, yet it is still a great sounding piece even today. The D-1 had a slew of radical innovations, and was the first high-performance one-box player during a time when everything else on the market used separate transport and D/A converter boxes. It remains something of a classic.
Our QB-9 was the world's first solid-state asynchronous USB DAC, which paved the way for the ongoing revolution in computer-based audio. It was entirely redesigned for the current ‘DSD’ version and is still one of the best sounding DACs available at any price.
A personal favorite is the design Ayre did for Neil Young's PonoPlayer. You've got a source that will store 500 CDs, play back both high-resolution PCM files and DSD, drives any set of headphones wonderfully, yet fits in your pocket and only costs a few hundred dollars. Its ability to communicate the musical intent of the artist is unparalleled at that price, and I know many people who have replaced their multi-thousand dollar CD players with it because it sounds better. To top it off, Pono has probably sold more players in one year than Ayre has total products in over twenty. To reach that many people and change their relationship to recorded music is very gratifying.
Hi-Fi+: What are two or three key aspects of digital audio that you wish consumers (and perhaps audio journalists, as well) better understood? Why?
CH: Adding a feature with digital technology is easy. Translating that into the analog world in a way that grabs our emotions is a much more elusive goal.
There's an old saying, “Performance, features, price – pick any two.” That's obviously what separates high-performance audio from the mainstream products. Yet with digital audio it becomes both easy and cheap to add features. People go down their checklist of desired features to make sure all of the boxes are ticked.
There are so many features today that many people tend to think of performance as just another feature. A feature is a quantifiable thing. A product either has remote control or it doesn't. Performance is something else altogether.
Many people try to reduce performance to something like a feature when they attach numbers to things. "What is the maximum sampling rate?", or "What is the signal-to-noise ratio?", or "How many picoseconds of jitter does it have?" None of these numbers will give the slightest clue as to how something actually sounds — or more importantly, how it will make you feel when you listen to music through it.
The true function of a music playback system is to deliver music on command. We play live music and go to concerts to hear our favorite artists live because that experience allows us to feel something deeply fundamental. Music is a uniquely human experience. The latest research shows that it even predates language — in fact it could even be said that music is what makes us human.
To be able to capture that experience and re-experience it on command by simply pressing a button is not merely a feature. It is actually something closer to a miracle. We are very lucky to live in such times.