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 -19. 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: 126/172W (21.0/22.4 dBW)
5 channels driven (8 ohms): 89W (19.5 dBW)
7 channels driven (8 ohms): 68W (18.3 dBW)
Distortion at 1 watt (THD+N, 1 kHz)
8/4 ohms: 0.03/0.03%
Noise level (A-wtd): –75.6 dB
Excess noise (with sine tone)
16-bit (EN16): 0.3 dB
Frequency response: 20 Hz to 20 kHz +0.2, –0.1 dB
STEREO PERFORMANCE, MULTICHANNEL INPUT
STEREO PERFORMANCE, DIGITAL INPUT
My test bench results for Cambridge’s Azur 551R reflect outstanding performance on almost every test. Noise, distortion, and especially linearity and digital-accuracy tests were all within one or two tenths of a decibel of theoretical targets, the only exception being analog-domain SNR, which was a few decibels weaker than the finest we’ve seen. “Excess noise,” the catchall test David Ranada devised to snapshot digital-conversion performance, was about as tight as I’ve measured. The 551R also qualified as the first receiver I’ve measured to nail “reference output level” at exactly the same volume-knob setting for all three modes: PCM-stereo and Dolby Digital -20 dBFS, and analog signal (200 mV). This has no particular qualitative value, but it suggests that somebody was sweating the small stuff, too — good for them.
As for power, the Cambridge handily beat its claimed specs, whether stereo or multichannel. In doing so, it showed me that the 551R’s central, forced-air cooling tunnel works well, with the fan indeed only coming on after sustained multichannel, high-power demand.
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