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 -3. All level trims at zero, except for subwoofer-related tests; all speakers were set to “large” with subwoofer on. All are worst-case figures where applicable.
Output at clipping (1 kHz into 8/4 ohms)
Distortion at 1 watt (THD+N, 1 kHz): 8/4 ohms: 0.04/0.06%
Noise level (A-wtd): –75.0 dB
Excess noise (with sine tone): 16-bit (EN16): 0.8 dB
Frequency response: 20 Hz to 20 kHz +0, –0.3 dB
STEREO PERFORMANCE, ANALOG INPUT
Reference input and output level is 200 mV; volume setting for reference output level was -2.
STEREO PERFORMANCE, DIGITAL INPUT
Reference level is –20 dBFS; all level trims at zero. Volume setting for reference level was -3.
Output at clipping (1 kHz, 8/4 ohms, both channels driven): 116/179W (20.6/22.5 dBW)
Distortion at reference level: 0.03%
Linearity error (at –90 dBFS): -0.5 dB
Noise level (A-wtd): –75.3 dB; with 96-kHz/24-bit signals: –83.9 dB
Excess noise (with/without sine tone)
Frequency response: <10 Hz to 20 kHz +0, –0.2 dB; with 96-kHz/24-bit signals: +0, -0.5 dB at 43.7 kHz
Measured results obtained with Dolby Digital test signals.
The VSX-60 produced a highly satisfactory set of test-bench numbers. Power output was particularly impressive for a compact, lightweight design, easily bettering the maker’s 90-watt rating on single- and two-channel tests and very nearly matching it on 5-channel (and coming respectably near on 7-channel). Just about everything else was excellent, with noise and D/A linearity both within a half-decibel or so of the ideal, and quite decent analog stereo-input results. (The VSX-60 has no analog-multichannel input.)
A note for the geek-inclined: I have altered my test setup for Class D amplifiers, yielding very slightly more accurate results. If we all went back over my earlier Class D design reports and subtracted, say, 0.1-0.2% from distortion measurements, and perhaps 0.4 dB from noise measurements, we probably wouldn’t be far off.
Since you asked: Class D power amplifiers all have significant levels of their switching frequency (usually, several hundred kilohertz) on their outputs. Loudspeakers will by nature ignore this, but its influence in the octave or so above the highest frequency of interest (20-40 or 45-90 kHz) is usually enough to affect bench results slightly. Consequently, measuring these amps requires adding a “brickwall” filter at some frequency immediately above the highest frequency of interest, to strip off residual ultrasonics from the switching frequency that may still be within the measurement bandwidth. There are a few different ways to do this; I just improved mine slightly. — D.K.
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