Test Report: Cambridge Audio Azur 551R A/V Receiver Page 4


Test Bench: Cambridge Audio Azur 551R A/V Receiver


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


  • 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): –80.1
  • Frequency response: <10 Hz to 160 kHz +0, –3 dB


  • Reference level is –20 dBFS; all level trims at zero. Volume setting for reference level was -19.
  • Output at clipping (1 kHz, 8/4 ohms, both channels driven): 123/135 W (20.9/21.3 dBW)
  • Distortion at reference level: 0.02%
  • Linearity error (at –90 dBFS): -0.1 dB
  • Noise level (A-wtd): –75.4 dB
  • With 96-kHz/24-bit signals: –84.5 dB
  • Excess noise (with/without sine tone)
  • 16-bit (EN16): 0.5/4.25 dB
  • quasi-20-bit (EN20): 10.3/10.4 dB
  • Noise modulation: 0.3 dB
  • Frequency response: <10 Hz to 20 kHz +0.2, –0.1 dB
  • With 96-kHz/24-bit signals: +0.2, -3 dB at 44 kHz


  • 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): 3.5v (72.v trimmed +6 dB)
  • Subwoofer distortion (from 6-channel, 30-Hz, 0-dBFS signal; subwoofer trim set to 0): 0.17%
  • 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

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.