One of the few surround-sound receivers that doesn't suffer from "feature creep"
British hi-fi used to be quirky. Anyone who remembers, say, Connoisseur turntables, Leak amps, or Quad speakers will know what I mean. Today’s Brit-fi, however — at least as exemplified by Cambridge Audio — has successfully transitioned from quirky to distinctive.
Take Cambridge’s new marquee A/V receiver, the Azur 751R. Although it’s assembled in China (like most large-production technology items today), the 751R was British-engineered at Cambridge’s London design studio. And while not particularly eccentric, the Azur’s design is British enough to eschew almost entirely the standard-issue feature-creep that burdens most A/V receivers, for one that is clean, simple, and reasonably compact.
Setup
A/V receiver installation in the HDMI era is a fairly generic task: Connect the cables, the speakers, and the auto-calibration mike and you’re pretty much there. (I still hook up a sampling of composite-, component-, and S-video links to check any video-processing features. Unlike many other receivers today, the 751R includes all three.)
The 751R was no exception. Its auto-setup and equalization features come in the form of Audyssey 2EQ, a simplified system engineered for less-powerful audio-DSP chips. Audyssey 2EQ takes data from only three calibration-mike positions (as opposed to MultEQ’s eight), applies lower-resolution filtering to full-range channels, and does not perform filtering to the subwoofer channel at all. I’m a bit surprised Cambridge didn’t spring for the substantially more capable Audyssey MultEQ found on many a price-competing and even far cheaper model, but everybody’s gotta save somewhere. (The 751R does incorporate Audyssey Dynamic Volume and Dynamic EQ features.)
Attentive readers may notice that, at least on paper, the 751R looks quite similar to the Cambridge Audio Azur 551R we reviewed last year. It is, with a couple of significant distinctions. The 751R specifies twice the amplifier power (120 watts, 7 channels driven, vs. the 551R’s 60 watts); more importantly, it adds vast audio-DSP horsepower, with no fewer than five large-scale chips from Cirrus and TI. Three of these are dedicated to A/D conversion and to upsampling all audio to 192 kHz/24-bit status, using technology from Swiss firm Anagram Technologies via a high-zoot interpolative filter that Cambridge claims enhances resolution and eliminates timing jitter.
Performance
There’s a certain class of audio-reviewer statement that I’m extremely leery of, and here comes one: Everything I listened to via the 751R, from the CBS Evening News to big-budget Blu-rays, sounded great, with a subtly relaxed clarity that my ears found addictive.
Can I quantify this? No. Did I perform level-matched A/B comparisons with other receivers, double- or at least single-blind? No. (Such comparisons are wholly impractical, at least in my studio.) Do I have one shred of hard evidence that Cambridge’s receiver is in any technical sense “better” than some other receiver or amplifier? No. Does it have anything at all to do with Cambridge’s massively DSP’d upsampling audio technologies? I have no idea.
Such are the hazards of audio criticism. What I can say (or repeat) is that the 751R sounded lovely every time I switched it on. Two-channel recordings like old friend Bonnie Raitt’s latest, Slipstream (on an 88.1/24 high-rez download from HDtracks.com — and yes, I pay for these), produced the kind of distinct, detailed timbres and “open-weave” sonic textures I expect from my stand-mount 2-way monitors, when they’re doing their best work with the best recordings. Raitt’s version of Bob Dylan’s “Standing in the Doorway” (late Dylan, from 1997’s Time Out of Mind) features a deceptively simple texture built up of heavy, deep bass, a very loose kick drum, languorous pedal-steel, Bonnie’s own peerless legato slide playing, and delicate snare brushwork. Yet every element was distinctly present, and easily teased out by the ear, if it chose. Mine found the brushed snare and deep drum to be particularly convincing, and Raitt’s hard-used but still-liquid voice was reproduced with impressive finesse.
Moving on to cinema sound, I elected to go big from the start with a shiny new Blu-ray of The Hobbit: An Unexpected Journey. I just can’t get enough of those lovable Halflings, though I found the movie to be noisy, repetitive, long, and generally tiresome. Nonetheless, it provides yet another reference-grade soundtrack from the Peter Jackson blockbuster mills, and the Cambridge was ready and eager to display it to full effect.
And I do mean “effect”: The 751R easily delivered the loudest scenes with full impact at true-cinema levels, even while retaining all the detail and easy openness I’d noted on music. The Cambridge’s surround palette is limited to the complete Dolby and DTS menus for multichannel and encoded signals; no “Thrill Theater” or “Disco” settings here. But this includes Dolby PLIIz processing with its height channels, and these couldn’t ask for a better demo than The Hobbit’s chase through the Orc mines (Chapter 27, on a set apparently borrowed from Indiana Jones and the Temple of Doom), where they added dramatically to the many vertiginous vertical effects.
Cambridge incorporates full video processing and scaling in the 751R. This aced my usual rotation of scenes and test patterns, upconverting (up to 1080p) and transcoding from composite-, component-, and S-video sources without incident. (This is hardly surprising, since Cambridge employs Anchor Bay’s ABT2010 chip for the number-crunching, an upgrade from the Azur 551R receiver’s Faroudja DSP, itself a solid performer. The same chip has appeared in numerous well-regarded video components from Oppo Digital and others.) You can choose to bypass or process individually by input, and set the usual video parameters (such as contrast, detail, and so on) for processed ones. The 751R has no provision for 4K video upconversion — something that the Asian makers’ flagships mostly now do.
Ergonomics
Cambridge’s marketing materials make it clear that the Azur line is about sound (and video) quality, not features. That’s fine: In day-to-day use, the 751R is a turn-it-on-and-forget-it pleasure that will regularly demonstrate the truth of this claim.
Nevertheless, for almost everything I loved about the 751R’s sound (and vision) usability-wise, I could find something I felt ambivalent about. The onscreen menus for setup and calibration are plain, clear, and easily followed text — but there are none for in-line use, not even any pop-ups to display helpful info like volume, listening-mode, or mute changes, nor channel-level adjustments, signal-format, or any other data.
Such onscreen aids are non-essential (if convenient — I’ve come to depend on them), as all this stuff appears on the front-panel display. But that low-contrast (though sexy) blue-on-black affair proved difficult or impossible to decipher from my listening chair about 11 feet distant, even when I was wearing my new, blisteringly expensive, computer-optimized progressive-lens specs.
Speaking of channel-level adjustments, making any such changes on the 751R is a project: There’s no provision to do so anywhere other than the main speaker-setup menu page, a 30-second round trip, and the opaque menu obscures the whole TV screen, though sound remains active.
And speaking of the remote, while it’s a very handsomely crafted brushed-aluminum item, its ergonomics are less lovely. There’s no key illumination, the buttons are small, and their labels are smaller, such that in dim light I struggled to read them even with my new glasses. (C’mon, who buys a $2,700 A/V receiver? Middle-aged, successful men, that’s who. And how many Just for Men users without reading glasses do you know?)
As mentioned, there’s no facility for streaming content, though the 751R does have an asynchronous USB port for playing up to 192/24-rez computer audio files, with the receiver acting as an outboard DAC/amplifier. In that case, however, you have to select the content and control its playback from your computer.
Sure, you probably already have streaming via your Blu-ray player or set-top box. But the 751R’s competition mostly now includes wired or even wireless onboard streaming at one-third the price or even less. There’s no Bluetooth, either — no great loss in my book if you value sound quality, which doubtless was Cambridge’s conclusion, too. Cambridge does provide Apple iDevice connectivity, but only through an optional hardware dock. You get basic control via the 751R’s remote, though you first have to go through a rather Byzantine remote-“pairing” process.
Like virtually all A/V receivers today, Cambridge’s flagship incorporates source-independent second-zone routing of stereo audio, along with composite-/S-video. However, the 751R adds a component-video output for second-zone HD potential, as well as a dedicated subwoofer output for 2.1-channel audio; you can even select a stereo-downmix signal from a digital/HDMI source. The 751R’s IR-repeater and 12-volt-trigger facilities are also unusually flexible, and the receiver comes with a card-style, dedicated, second-zone remote, a very welcome convenience.
Bottom Line
Cambridge Audio’s Azur 751R is beautifully built and meticulously finished — and its price reflects it. None of my ergonomics-related grumblings above should take away from the truth that its audio/video performance was powerful, pristine, and without any weaknesses I could uncover. If your ideal of A/V system architecture is a setup that you tweak and calibrate only once and then simply use day-to-day, adjusting little beyond the volume control — and if cost is not an overwhelming consideration — you will be pleased. Delighted. Thrilled. Yes, the Azur 751R sounds that good.
Test Bench / Power Output
When I tested Cambridge’s Azur 551R receiver just about a year ago, I found superb performance throughout. The new, more powerful 751R matched that feat nearly perfectly (the one exception being D/A linearity, which I’ll return to) while adding a substantial power boost. The 751R looks extremely similar to the 551R and is not all that much larger (about 1.5 inches), yet our review sample produced almost 2 dB more power in every test — including the most challenging, all-7-channels one, where the 751R posted an impressive 125 watts with all channels at their clipping point simultaneously.
Noise, distortion, and frequency response were all exceptionally good across the board, as was true with the earlier model. However, as I alluded to above, the 751R’s digital-to-analog linearity — that is, its amplitude accuracy with very small signals reflecting the 2 or 3 “least significant” bits of digital words — was actually inferior to that of the less expensive 551R. The 751R’s linearity was essentially perfect at –70 dBFS, but it showed error of around 6 dB at –90 dBFS, which suggests a rounding error or possibly a time-domain equivalent (time and amplitude are inextricably intertwined in massively oversampling converters like the Cambridge’s). Thus, and almost certainly in consequence, the 751R’s signal-to-noise results and S&V-specific “excess noise” ranged from 0.5 dB to a few dB inferior to the earlier model’s. This is not such a big deal since we’re on the ragged edge of theoretical perfection here anyway, and it does nothing to counter my very positive response to the Cambridge receiver’s audible performance, which was outstanding.
DOLBY DIGITAL PERFORMANCE
All data were obtained from various test DVDs using 16-bit dithered test signals, which set limits on measured distortion and noise performance. Reference input level is –20 dBFS, and reference output is 1 watt into 8 ohms. Volume setting for reference level was –18. All level trims at zero, except for subwoofer-related tests; all speakers were set to “large,” subwoofer on. All are worst-case figures where applicable.
Output at clipping (1 kHz into 8/4 ohms)
1 channel driven: 239/325W (23.8/25.1 dBW)
5 channels driven (8 ohms): 146W (21.6 dBW)
7 channels driven (8 ohms): 125W (21 dBW)
Distortion at 1 watt (THD+N, 1 kHz), 8/4 ohms: 0.03/0.03%
Noise level (A-wtd): –74.7 dB
Excess noise (with sine tone),16-bit (EN16): 0.6 dB
Frequency response: 20 Hz to 20 kHz<br>+0.1, -0 dB
STEREO PERFORMANCE, MULTICHANNEL INPUT
Reference input and output level is 200 mV; volume setting for reference output level was –19.
Distortion (THD+N, 1 kHz, 8 ohms): 0.03%
Noise level (A-wtd): –81.1
Frequency response: <10 Hz to 160 kHz: +0, –3 dB
STEREO PERFORMANCE, DIGITAL INPUT
Reference level is –20 dBFS; all level trims at zero. Volume setting for reference level was –17.5.
Output at clipping (1 kHz, 8/4 ohms, both channels driven): 208/273W (23.2/24.4 dBW)
Distortion at reference level: 0.02%
Linearity error (at –90 dBFS): 6 dB (see Notes)
Noise level (A-wtd): –74.9 dB
with 96-kHz/24-bit signals: –84.5 dB
Excess noise (with/without sine tone)
16-bit (EN16): 0.8/5.0 dB
quasi-20-bit (EN20): 10.5/11.3 dB
Noise modulation: 0.4 dB
Frequency response: <10 Hz to 20 kHz; 0.1, –0 dB
with 96-kHz/24-bit signals:<br>+0.2, -3 dB at 44.3 kHz
BASS-MANAGEMENT PERFORMANCE
Measured results obtained with Dolby Digital test signals.
Subwoofer-output frequency response (crossover set to 80 Hz): 16 dB/octave (approx.) above –3-dB rolloff point of 80 Hz
High-pass-filter frequency response (crossover set to 80 Hz): 12 dB/octave below –3-dB rolloff point of 80 Hz
Maximum unclipped subwoofer output (trim at 0): 3.7V
Subwoofer distortion (from 6-channel, 30-Hz, 0-dBFS signal; subwoofer trim set to 0): 0.2%
Crossover consistency: bass crossover frequency and slope were consistent for all sources and formats.
Speaker size selection: all channels can be set to “small.”
Speaker-distance compensation: available for all main channels.
Notes
When I tested Cambridge’s Azur 551R receiver just about a year ago, I found superb performance throughout. The new, more powerful 751R matched that feat nearly perfectly (the one exception being D/A linearity, which I’ll return to) while adding a substantial power boost. The 751R looks extremely similar to the 551R and is not all that much larger (about 1.5 inches), yet our review sample produced almost 2 dB more power in every test — including the most challenging, all-7-channels one, where the 751R posted an impressive 125 watts with all channels at their clipping point simultaneously.
Noise, distortion, and frequency response were all exceptionally good across the board, as was true with the earlier model. However, as I alluded to above, the 751R’s digital-to-analog linearity — that is, its amplitude accuracy with very small signals reflecting the 2 or 3 “least significant” bits of digital words — was actually inferior to that of the less expensive 551R. The 751R’s linearity was essentially perfect at –70 dBFS, but it showed error of around 6 dB at –90 dBFS, which suggests a rounding error or possibly a time-domain equivalent (time and amplitude are inextricably intertwined in massively oversampling converters like the Cambridge’s). Thus, and almost certainly in consequence, the 751R’s signal-to-noise results and S&V-specific “excess noise” ranged from 0.5 dB to a few dB inferior to the earlier model’s. This is not such a big deal since we’re on the ragged edge of theoretical perfection here anyway, and it does nothing to counter my very positive response to the Cambridge receiver’s audible performance, which was outstanding. —D.K.
