Ayre Acoustics QA-9 USB A/D converter

Since its founding in 1993, Colorado-based Ayre Acoustics has made its name with amplifiers and preamplifiers based on truly balanced, solid-state circuitry that didn't use the ubiquitous panacea of loop negative feedback to produce linear behavior. Their first digital product was the D-1x DVD player, reviewed for Stereophile by Paul Bolin in February 2003, which offered unusually good video performance. The D-1x was followed by the C-5xe and DX-5 universal players, respectively reviewed by Wes Phillips (July 2005) and Michael Fremer (December 2010). But the most intriguing digital product to come from Ayre was the QB-9 digital processor. Reviewed by WP in October 2009, the QB-9 has just one input, USB, and uses Gordon Rankin's proprietary Streamlength code to give asynchronous operation, which in theory offers the best jitter suppression. "The QB-9 isn't a computer peripheral," said Ayre's marketing manager at that time, Steve Silberman. "It makes computers real high-end music sources"—a statement with which WP agreed.

Then, at the 2011 Rocky Mountain Audio Fest, I was given a dem of what I at first assumed was a QB-9—until I saw the bar-graph level meters to either side of the sample-rate display. This was the QA-9, a high-performance analog/digital converter, housed in the same chassis as the QB-9 and intended to allow audiophiles to make rips of their LPs of the highest quality possible.

The QA-9 operates at sample rates up to 192kHz, outputting 24-bit data either by a USB 2.0 connection or by AES/EBU. (The two aren't operational at the same time.) The basic version costs $3950; a Pro version, which includes DSD and Word Clock outputs on transformer-coupled BNC jacks, costs $4750. Given my extensive experience of both domestic and professional A/D converters, which has convinced me that the most critical process in digital recording is the initial analog/digital conversion—nothing downstream can put right whatever was done wrong in that conversion (footnote 1)—I asked for a production sample of the QA-9.

Design Philosophy
Via e-mail, I asked Ayre's founder and designer, Charlie Hansen, why a manufacturer exclusively known for its domestic high-end audio products had ventured into a field dominated by pro-audio companies.

"If we build, say, a great preamplifier, then one audiophile will be able to bliss out on the music. On the other hand, if we build a great A/D converter, then literally millions of people could benefit from the improved sound. Several professionals own Ayre equipment, usually for their home systems. Somewhat typical but most notable is Rick Rubin [record producer and founder of American Recordings and Def Jam Records]. He says that Ayre makes the best-sounding digital playback gear, and he has been after us for years to build equally good-sounding recording gear.

"To my knowledge, nobody has ever built an ADC with fully discrete, fully balanced, zero-feedback analog circuitry. In my experience, the single most important factor in getting good sound in digital audio is with the analog circuitry, so that was reason enough to start the project. Of course, we at Ayre are never content to rest on our laurels, so we also incorporated a slew of other innovations."

The heart of the QA-9 is the AT1201, a two-channel A/D converter chip that is new to me, from a company also new to me: Arda Technologies. The chip's datasheet describes it as an "advanced multi-bit sigma-delta" converter that will operate up to a sample rate of 384kHz with an astounding dynamic range of 124dB.

"Arda does consulting work for big contractors. They are audiophiles, and in their spare time designed and built a new A/D chip that clearly outperforms anything from the competition. Specifically, the out-of-band noise is ridiculously low, and this gave us a lot of freedom to 'think different' (as Apple ungrammatically said a couple of decades ago)."

What did Hansen mean by "think different"?

"Ever since DSD was announced, it has received uniformly positive comments on the sound quality. . . . [T]o be honest, we were basically baffled by Sony's original marketing material. We couldn't figure out how the system worked, let alone why it sounded good. But over the years, not only did more and more information leak out, but our understanding of digital audio at Ayre grew rapidly.

"In short, the reason that DSD sounds as good as it does is because there is no filtering done on the record side. The playback side requires a filter (per the Scarlet Book specs), but compared to the brick-wall filters used in typical PCM products, this is a much, much gentler affair. When we developed the QB-9 we spent nearly four months performing listening tests on digital filters. It was clear that both the anti-aliasing (record) and reconstruction (playback) filters had a very strong influence on the sound of digital audio (remember how the 'non-oversampling' DACs were quite popular for a few years?), and so we wanted to really understand what was going on. . . .

"The relatively recent advent of using the personal computer as a way to store and play back music files has changed the game entirely. Now we can buy, store, and play back music at quad-sample rates [176.4 and 192kHz] (or even higher), if so desired. But the problem is that digital audio equipment is still designed by digital audio engineers, traditional engineers, who, if they are using a 192kHz sampling rate, are going to make their equipment with flat frequency response to 96kHz and then just put a brick-wall filter on it. Fortunately, I am not a traditional digital audio engineer! I therefore have the freedom to ask 'Why?,' and I do that a lot!

"So for the QA-9 in Listen mode, we decided that the goal was to make the converter operating at the quad-sample rate to perform more or less like a perfect 30ips analog tape machine. The frequency response is down about –3dB at 50kHz, but it goes down to around 1Hz with no 'head bumps' to worry about. There is zero wow and flutter, and the distortion and noise are about an order of magnitude better (ie, 20dB) than the best analog tape machines.

"Yes, the anti-aliasing filter (in Listen mode) is down only about 20dB at the aliasing point of 96kHz, but is that really a problem? Do any recordings actually have any meaningful amount of musical energy up at 172kHz, where there would be aliasing that would fold down into the audioband?

"Of course not! There aren't many instruments with significant amounts of energy above 90–100kHz. Nor are there many microphones with any significant response this high. Or mike preamps. Or mixing boards. Or whatever.

"So the first thing that we did was to use a completely different type of digital filter at the output of the delta-sigma converter. (Every audio ADC chip made for the last 20 years has been a delta-sigma type, as the competing successive-approximation devices died off long ago.) Instead of using the normal low-pass Finite Impulse Response (FIR) filter to turn the output of the delta-sigma DAC into PCM, we use a moving-average filter. This doesn't just allow for improved transient response, but actually perfect transient response. And since we are starting with a 256Fs [11.2896MHz] sample rate, we don't have the problems exhibited by 'non-oversampling' DACs that also have 'perfect' transient response. There is no pre-ringing, no post-ringing—no ringing whatsoever. (This is in the Listen mode at both the quad and double sampling rates. It is not possible to use this trick at the single sample rate, where instead we use a more conventional FIR low-pass filter, but of course this is a slow-rolloff design to minimize ringing, and also is a minimum-phase design, so that all of the ringing occurs after the transient, with no unnatural 'pre-echo' before the transient occurs.)



Footnote 1: I haven't forgotten Meridian's implementation of Peter Craven's "apodizing filter," which replaces the original A/D converter's acausal ringing at the Nyquist Frequency with post-impulse ringing at a very slightly lower frequency. But there are many other ways for A/D converters to misbehave.
COMPANY INFO
Ayre Acoustics, Inc.
2300-B Central Avenue
Boulder, CO 80301
(303) 442-7300
ARTICLE CONTENTS
Share | |
COMMENTS
JR_Audio's picture

Hi John.

A nice review on a sort of “untypical” HiFi product (AD Converter) with some very good aspects from Charles Hansen about Digital Filter

Juergen

PS: I have had also the Metric Halo ULN-2, because of the good reputation, but was not happy with the sound and so sold it after 1 month.

mav52's picture

John, have you tried any of the Symmetricom timing analyzerers like,  TimeMonitor Suite etc.. for measuring jitter ?

John Atkinson's picture

Quote:
have you tried any of the Symmetricom timing analyzerers like,  TimeMonitor Suite etc.. for measuring jitter ?

Sorry, no.

John Atkinson

Editor, Stereophile

Staffan Fritz's picture

Hi John,

Thanks for reviewing an A/D-converter - not many of those reviews around!

What I would like to see in Stereophile is an article covering the hardware in different price brackets necessary to rip vinyl, as A/D-converters and, especially, the stage between the turntable and the converter. It's difficult enough to choose between all the available phono amplifiers, but what if you want to apply the RIAA curve in the digital domain: what then to use? How much do you have to invest to gain anything compared to using your existing phono stage that cannot bypass the RIAA filter? What about using a tape deck to amplify the signal so that you can use a line input? Or is a microphone amplifier the way to go, and then what about impedance and what not (I'm totally lost there).

Thanks for a very entertaining magazine; one of the true highlights of the month even if most of the reviewed equipment is way out of my reach. But I enjoy it all the same!

Staffan Fritz

Visby, Sweden

X
Enter your Stereophile.com username.
Enter the password that accompanies your username.
Loading