As seems usual for Onkyo, the TX-SR605 showed just how technically accomplished mass-produced electronics can be today, with perfectly flat frequency response and perfect D/A linearity to -90 dB (and beyond). Both are as good results as I've measured, and while my memory isn't infallible, I believe this to be the first time these two particular aces have been drawn by the same unit. The Onkyo's S/N results on our dithered-silence tests were slightly "better-than-perfect" in theoretical terms (-75.6 being the pure-dither result), which suggests a slight shortfall of its LSB (lowest significant bit) magnitude; probably not meaningful in any audible sense. (Like most units that measure similarly, the error was greater for Dolby Digital than for PCM digital signals; I've never been able to figure out why this should be, but have observed it more than a few times.)
Power results were fairly typical for a mid-market A/V receiver. The TX-SR605 met its single-channel and stereo specs handily enough, but fell short when 5 or 7 channels were stressed simultaneously, and protected itself to about one-third power, presumably via current-limiting circuitry, when asked to do so for more than a few hundred milliseconds. This almost certainly has very little audible impact - the receiver played 7 channels happily enough at 1 dB short of clipping for many minutes at a time. This design approach, which we see often, probably reflects the manufacturer's attempt to hold down power-supply costs and is sensible enough in real-world terms, where 5 or 7 channels probably never demand full power simultaneously for more than a tenth of a second at a time.
All data was 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 75. 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: 144/217 W (21.6/23.4 dBW)
5 channels driven (8 ohms): 85 W* (19.3 dBW)*
7 channels driven (8 ohms): 80 W* (19 dBW)*
Distortion at 1 watt (THD+N, 1 kHz)
8/4 ohms: 0.02/0.03%
Noise level (A-wtd): -77.9 dB
Excess noise (with sine tone)
16-bit (EN16): 1 dB
Frequency response: 20 Hz to 20 kHz +0, -0.0 dB
*With more than four channels stressed to clipping simultaneously for durations greater than a few hundred milliseconds, the TX-SR605 protected itself to about one-third power, presumably via current-limiting circuitry. Reducing drive level for a few minutes, or power-cycling the unit, restored normal operation.
Reference input and output level is 200 mV; volume setting for reference output level was 77.
Distortion (THD+N, 1 kHz, 8 ohms): 0.01
Noise level (A-wtd.): -82.7
Frequency response: <10 Hz to 166 kHz +0, -3 dB
Reference level is -20 dBFS; all level trims at zero. Volume setting for reference level was 78.
Output at clipping (1 kHz, 8/4 ohms, both channels driven): 124/175 W (20.9/22.4 dBW)
Distortion at reference level: 0.02%
Linearity error (at -90 dBFS): 0.0 dB
Noise level (A-wtd): -75.9 dB
with 96-kHz/24-bit signals: -87.7 dB
Excess noise (with/without sine tone)
16-bit (EN16): 0.8/0.8 dB
quasi-20-bit (EN20): 10.7/11.5 dB
Noise modulation: 1.2 dB
Frequency response: <10 Hz to 20 kHz +0, -0.0 dB
with 96-kHz/24-bit signals: <10 Hz to 46 kHz +0, -3 dB
Measured results obtained with Dolby Digital test signals.
Subwoofer-output frequency response (crossover set to 80 Hz): 24 dB/octave (approx.) 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): 7.4v
Subwoofer distortion (from 6-channel, 30-Hz, 0-dBFS signal; subwoofer trim set to 0): 0.03%
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"
Speaker-distance compensation: available for all main channels.
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