Cambridge Audio Azur 851D D/A processor

When I think of Cambridge Audio today, it sits firmly in the category of Value with a capital V. After spending the past decade figuring out how to balance price with performance, to give budding audiophiles entry points to better sound, in 2012 they began pushing the upper end of their value envelope with the Azur 851 series of products, of which the Azur 851D upsampling DAC and digital preamplifier ($1649) is the latest model.

I've enjoyed having one of Cambridge's integrated amps in my office system for years, and the company boasts that the 851 series, designed in the UK and manufactured in China (like the rest of their line), is the best they've produced so far. After spending the last year listening to domestically manufactured DAC-preamps costing $6000 and up, I was curious to hear how a product costing only a quarter of the bottom of that range might stack up.

Your Basic Black Jacket
The Azur 851D is one of the more normal-looking DACs I've reviewed: its standard, rectangular black case (also available in silver) is 16.8" wide, 4.5" high, and 14" deep. Its conventional and rather plain, even minimal look will either be a bonus in a system where you want the components to stack in orderly fashion and disappear, or might disappoint dressed in such a traditional jacket when hanging out in public. If you do like a tidy stack of discreetly matching products, Cambridge Audio's Azur 851 line now includes the 851E preamp, the 851A integrated, the 851P power amp, and the 851C DAC-CD-preamp.

Nonetheless, the 851D's basic coat and tie are very nice: build quality is solid, with a thick, though not gratuitously so, faceplate and a removable, brushed-metal top plate with ventilation grilles left and right. Fit'n'finish are superb all around; other than the rather plain look, the 851D doesn't present as a budget model. A nice touch is the shiny silver outlining the display and each control and jack on the front panel.

During use, the top vents emitted enough heat that I'd hesitate to put the 851D under other components in a fully enclosed cabinet, but it was never more than warm to the touch when placed outside. The nicely finished case is well damped, and the 851D weighs a hefty 16.5 lbs.

On the left of the rear panel are the grounded IEC power socket and power switch, and an RS-232C port for custom control setups. Next to those are the control connections for trigger out, IR emitter in, and Control Bus in and out. In the center of the rear panel are the 851D's 10 (!!!) digital inputs and its TosLink and S/PDIF digital outs. The inputs include: USB Type B (with ground-lift switch if there is hum, something I've never seen before), BNC, AES/EBU, four TosLink (two TosLink are in parallel with coaxial S/PDIF inputs, and, finally, a USB Type A jack for an optional BT100, aptX-compatible Bluetooth adapter (included with my review sample). I'll talk more about 851D's Bluetooth function later, but it's interesting to note that if you don't use it for audio, Cambridge says you can use this USB jack for charging devices such as phones, etc. Except for the TosLinks, which are limited to 24-bit/96kHz, all of these inputs accept up to 24/192 signals (USB must be set for Class 2.0 for sample rates >96kHz). On the right are the balanced (XLR) and unbalanced (RCA) analog audio outputs.


On the front panel, starting at the left, are the Standby button, a ¼" headphone jack, the Menu button, and the infrared sensor for the remote control. Above these are four indicator lights for the three reconstruction filter settings, which can be selected via the setup menu or with a button on the remote—a wonderful feature I'll talk more about later.

In the center is a large LCD display, flanked on each side by a column of four very small, unlabeled buttons with various functions, depending on which menu page is displayed. From an ergonomic point of view, I prefer this kind of interface to the more common Up/Down/Left/Right paddle with central Enter button. With the 851D, you simply press the Menu button until you see the page you want, then tap the tiny buttons along the sides to make your choices.

When in the setup menu, you'll see choices for configuring the USB input to Class 1 or 2, turning on and off the Preamp mode (ie, whether or not to use the volume control for the analog outputs), Front IR control (for custom systems), display brightness, trigger options, balance, and Auto Power Down settings. You can also rename the inputs, and assign to each a different filter and phase setting. I renamed Input 1 "Sooloos" and Input 2 "Disc," using the volume knob to select letters and the buttons to make choices. I left the filter for all inputs in the default Linear Phase setting, polarity not inverted, and switched those later with the remote while listening.

Once you're ready to play, the display will show you the eight input choices next to their buttons: S/PDIF or TosLink Inputs 1–4 (in my case Sooloos, Disc, Input 3, Input 4), BNC, AES/EBU, Bluetooth, and USB. At the bottom center of the screen I was pleased to see the sample rate displayed, or "No Input" if nothing is locked. If you're in Preamp mode, a large volume display appears above this, with an arc of bars and a numeric display indicating the level in dB. When adjusting balance, this display shows the left/right level ratio.

To the right of the display is the large, well-damped volume knob, which controls the analog and headphone but not the digital output levels. This knob also has various functions when you're in Setup mode. A nice touch: When you plug in headphones, the analog outputs are muted, and the volume display and knob then track the volume level for headphone listening.

The largish remote control has a small forest of buttons, most of which can be used with other Cambridge products. A simpler remote limited to such DAC functions as input select, filter options, and volume would have been nice, but this one did the job as long so I kept my glasses handy, and will probably be preferred if you have an all-Cambridge system.

A Variety of Matching Ties
For filtering operations, the Azur 851D includes the Analog Devices ADSP-BF532 BlackFin 32-bit DSP chip, which upsamples data to 24/384 using the second-generation Adaptive Time Filtering (ATF2) process. Digital-to-analog conversion is handled by two Analog Devices AD1955 24-bit chips, a step up from the Wolfson WM8740 DACs used in Cambridge's DacMagic Plus. Though the AD1955 can also support DSD bitstreams, there is no provision for that format with the 851D.

About those filter settings: A DAC's digital datastream needs to be converted to an analog audio signal to feed an analog preamp or power amp. That conversion process is fraught with ugly ultrasonic byproducts, and as yet no perfect filter has been designed that can remove these. This has led to different designs that make different tradeoffs.

Many designers of DACs simply choose the filter whose sound they prefer and design around it. Others, such as Cambridge Audio, provide choices with which the sound can be subtly tailored to the listener's particular system. The results can be subtle; if so inclined, you'll want to spend some time with varying types of music to sort through the variations to decide which you like best.

My review sample's default filter setting was Linear Phase. This prioritizes constant group delay of the signal, ensuring that all frequencies stay in perfect sync, but with the side effect of producing pre- and post-ringing.

The next filter is Minimum Phase, which introduces a very small amount of phase shift between the various frequencies, but eliminates pre-ringing. Finally, there's the Steep Filter, a variation of the Linear Filter that trades a bit of the ringing and ultra-high-frequency response for a filter that's more effective at eliminating the ultrasonic images that are a byproduct of the conversion process.

Bringing Out the Coloured Paisley Coat
Cambridge Audio was founded in England in 1968—they remind you of their Britishness all over the website—so it was a no-brainer to start pulling albums from that place and time to evaluate the Azur 851D.

From October 1968, "Get Thy Bearings," from Donovan's The Hurdy Gurdy Man (CD, Epic) seemed a good place to start. King Crimson played this song in concert early in their career, but here, on the original recording, we have acoustic bass and drums front and center, with Donovan's voice off to the right and acoustic guitar eventually joining on the left. As I've noted before, older, well-made analog recordings, if mastered properly, preserve the artifacts inherent in the original recording technology, and those details were abundant here. The Azur 851D lovingly reproduced the occasional smeared image, studio noise, and microphone overload—and, of course, the great music—without glare or veiling. Off to a good start.

Cambridge Audio
US distributor: Audio Plus Services
156 Lawrence Paquette Industrial Drive
Champlain, NY 12919