Test Bench: Cambridge Audio Azur 640R A/V Receiver

The Cambridge Audio Azur 640R was a pleasure to measure, as it consistently delivered expected behavior and declined to snap fuses, smoke circuit boards, or require resetting, despite the usual abuse. Better still, it also set new receiver benchmarks on test after test: perfect (yes, perfect!) scores for PCM-stereo linearity at -90 dB and real-world (dithered) signal-to-noise ratio (plus superb 96-kHz/24-bit S/N), best-ever excess-noise figures, and stereo output power that could probably sneak by on a "150 watts x 2" model. Multichannel Dolby Digital results were just as fine, and the Azur 640R did indeed deliver its full rated power with five channels driven before clipping - and very nearly did so with seven channels stressed. It's quite nice, once in a while, to have test-bench results (acquired, as always, after listening/writing is complete) coincide so well with listening opinions, reconfirming that maybe one really can hear a difference now and then.

DOLBY DIGITAL PERFORMANCE All data were obtained from various test DVDs using 16-bit dithered test signals, which set limits on measured distorting 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 were at zero, except for subwoofer-related tests, and 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: 166/235 watts (22.2/23.7 dBW) 5 channels driven (8 ohms): 109 watts (20.4 dBW) 7 channels driven (8 ohms): 91 watts (19.6 dBW) Distortion at 1 watt (THD+N, 1 kHz) 8/4 ohms: 0.02/0.03% Noise level (A-weighted): -75.8 dB Excess noise (with sine tone) 16-bit (EN16): 0.3 dB Frequency response: 20 Hz to 20 kHz +0.1, -0.3 dB

MULTICHANNEL PERFORMANCE, ANALOG INPUT Reference input and output level is 200 mV; volume setting for reference output level was -19 dB. Distortion (THD+N, 1 kHz, 8 ohms): 0.005% Noise level (A-weighted.): -91.7 dB Frequency response: <10 Hz to 130 kHz +0, -3 dB

STEREO PERFORMANCE, DIGITAL INPUT Reference level is -20 dBFS; all level trims at zero. Volume setting for reference level was -19 dB. Output at clipping (1 kHz, 8/4 ohms, both channels driven): 145/197 watts (21.6/22.9 dBW) Distortion at reference level: 0.02% Linearity error (at -90 dBFS): 0 dB Noise level (A-weighted): -75.7 dB with 96-kHz/24-bit signals: -90.4 dB Excess noise (with/without sine tone) 16-bit (EN16): 0.1/0.1 dB quasi-20-bit (EN20): 6.4/5.9 dB Noise modulation: 0.3 dB Frequency response: 20 Hz to 20 kHz +0, -0.2 dB with 96-kHz/24-bit signals: 20 Hz to 42 kHz +0, -3 dB

BASS-MANAGEMENT PERFORMANCE Measured results obtained with Dolby Digital test signals. Subwoofer-output frequency response (crossover set to 80 Hz): 24 dB/octave above -6-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): 9.7 volts Subwoofer distortion (from 6-channel, 30-Hz, 0-dBFS signal; subwoofer trim set to 0): 0.1% Crossover consistency: bass crossover frequency and slope were consistent for all sources and formats Signal-format consistency: consistent for all applicable formats Speaker size selection: all channels can be set to "small" (if C=large, L/R also must be large) Speaker-distance compensation: available for all main channels, but L/R pairs fixed together

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