av Richard » 2011-07-18 08:55
Här är intressanta mätningar på den DS- spelare som Harryup just lånat hem, från stereophile:
"Turning to the Majik DS-I's performance as a D/A converter, I assessed this using the TosLink S/PDIF input. (I will publish a Follow-Up next month comparing its S/PDIF behavior with that via a wired Ethernet connection.) The digital input preserved absolute polarity and successfully locked to data with sample rates of up to 192kHz. Data representing a full-scale 1kHz tone gave a result at the Line Out jacks of 1.92V. The maximum distortion-free volume-control setting with this signal was "71," which gave a level of 40.5W into 8 ohms at the speaker jacks. A setting of "72" gave 49W, but with a THD figure of 2.33%.
Playing a dithered 1kHz tone at –90dBFS from CD while sweeping the center frequency of a 1/3-octave bandpass filter from 20kHz to 20Hz and looking at the signal at the Line Out jacks gave the spectra shown in fig.2. The traces peak at exactly –90dB, suggesting minimal linearity error, and with 24-bit data (bottom traces), the noise floor was approximately 10dB lower than it was with 16-bit data (top pair of traces). This implies a resolution of around 18 bits, which is sufficient to allow the Majik DS-I to correctly decode a dithered tone at –120dBFS (bottom traces). Repeating the analysis with an FFT technique gave the same result (fig.3), with almost no harmonic spuriae unmasked by the increase in bit depth.
Fig.2 Linn Majik DS-I, 1/3-octave spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with 16-bit data (top) and 24-bit data (middle), plus dithered 1kHz tone at –120dBFS with 24-bit data (bottom). (Right channel dashed.)
Fig.3 Linn Majik DS-I, FFT-derived spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit data (left channel cyan, right magenta), 24-bit data (left blue, right red).
The low noise floor and excellent linearity allowed the three DC levels described by an undithered sinewave at exactly 90.31dBFS to be readily resolved, with good waveform symmetry (fig.4), and 24-bit data gave a good representation of a sinewave (fig.5). Distortion via the digital input was very low, a full-scale tone being accompanied by just the second and third harmonics, at –98dB (0.0012%) and –106dB (0.0005%), respectively (fig.6). Similarly, intermodulation distortion was vanishingly low, the 1kHz difference product resulting from a full-scale mix of 19 and 20kHz tones lying at –103dB (0.0007%) in the right channel and –109dB (0.00035%) in the left (not shown).
Fig.4 Linn Majik DS-I, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left blue, right red).
Fig.5 Linn Majik DS-I, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left blue, right red).
Fig.6 Linn Majik DS-I
The Linn's rejection of jitter via its S/PDIF input was dependent on the source component. Via the RME soundcard in one of my test-lab PCs, a TosLink connection gave 454 picoseconds peak–peak of wordclock jitter, as assessed by the Miller Analyzer housed in the same PC. This was mostly due to sidebands at the data-related frequencies of ±229 and ±689Hz. However, these sidebands disappeared when the same 16-bit data were fed via TosLink from the Audio Precision SYS2722 (fig.7).
Fig.7 Linn Majik DS-I, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz, 16-bit S/PDIF data via 15' TosLink. Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz (left channel blue, right red).
Looking at the Majik DS-I's behavior as a conventional integrated amplifier, it offered a maximum gain of 47.9dB into 8 ohms, which is higher than average. The speaker output, Line Out, and Preamp Out were all non-inverting. The line input impedance was a constant 10.5k ohms at all frequencies, which agrees with the specification. The Line Out's source impedance was 444 ohms and the Preamp Out 297 ohms, both figures constant at all frequencies.
The output impedance at the speaker terminals was 0.16 ohm at low and midrange frequencies, rising slightly to 0.18 ohm at the top of the audioband, which results in a +0.2dB/–0.1dB modification of the amplifier's frequency response with our simulated loudspeaker (fig.8, gray trace). This graph also indicates that the DS-I's response is curtailed at both ends of the spectrum, reaching –1.5dB at 10Hz and 29kHz, and –0.5dB at 20Hz and 16kHz. This was not affected by the volume-control setting, but as a result, the Linn's reproduction of a 10kHz squarewave has longer risetimes than normal (fig.9), though there is no sign of overshoot or ringing."
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