Sidebar 3: Measurements
I measured the EMM Labs DV2 using my Audio Precision SYS2722 system (see the January 2008 "As We See It"), using the Audio Precision's AES/EBU digital output—unlike JVS, I had no problems with this input—and USB data sourced from my MacBook Pro running on battery power, with Pure Music 3.0 playing WAV and AIFF test-tone files.
Apple's USB Prober utility identified the EMM processor as "DV2 Reference DAC with MQA Decoder" from "EMM Labs," with the serial number "LAB0012." The DV2's USB port operated in the optimal isochronous asynchronous mode. Apple's AudioMIDI utility revealed that, via USB, the DV2 accepted 16- and 24-bit integer data sampled at all rates from 32 to 384kHz. The AES/EBU and coaxial and TosLink S/PDIF inputs all locked to datastreams with sample rates of up to 192kHz.
The volume control operated in accurate 0.5dB steps. With the volume control set to its maximum of "100," a 1kHz digital signal at 0dBFS resulted in a balanced output level of 4.26V into 100k ohms with the output level set to Low, and 7.25V with it set to High. (Except where indicated, all measurements were taken at the High setting.) The maximum unbalanced output levels were half the balanced levels, as expected. The output impedance was the same from both sets of analog outputs, at a moderately low 297 ohms from 20Hz to 20kHz, and both outputs preserved absolute polarity (ie, were non-inverting).
The DV2's impulse response with 44.1kHz data (fig.1) indicates that the reconstruction filter with this signal is a very short linear-phase type. With 44.1kHz-sampled white noise (footnote 1, fig.2, red and magenta traces), the DV2's response rolled off gently above 20kHz and didn't reach full stop-band suppression until 44.1kHz. Peculiarly, given this slow rolloff, the aliased image at 25kHz of a full-scale tone at 19.1kHz (blue and cyan traces) was still suppressed by more than 110dB. (Perhaps this was due to the DV2's reconstruction filter changing its behavior with this signal.) The second and third harmonics of the 19.1kHz tone are visible above the ultrasonic noise floor, though both are low in level.
Footnote 1: My thanks to Jürgen Reis of MBL for suggesting this test to me.
Fig.1 EMM DV2, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).
Fig.2 EMM DV2, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan), with data sampled at 44.1kHz (20dB/vertical div.).
When I examined the DV2's frequency response with data at 44.1, 96, 192, and 384kHz, its 44.1kHz output rolled off sharply above 20kHz (fig.3, gray and green traces). The responses at the three higher sample rates followed the same shape, flat to 20kHz, with then a slow rolloff, disturbed by a steeper drop at each Nyquist frequency. With data sampled at 384kHz, the DV2's output was down by 11dB at 120kHz. Channel separation was superb, at >120dB in both directions below 3kHz, and still 112dB at 20kHz (fig.4). The low-frequency noise floor was both low in level and commendably free from any power-supply–related artifacts (fig.5).
Fig.3 EMM DV2, frequency response at –12dBFS into 100k ohms with data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), 192kHz (left blue, right red), 384kHz (left blue, right green) (1dB/vertical div.).
Fig.4 EMM DV2, Channel separation (5dB/vertical div.)
Fig.5 EMM DV2, spectrum (0Hz–1kHz) of dithered 1kHz tone at 0dBFS (20dB/vertical div.).
When I increased the bit depth from 16 to 24 with a dithered 1kHz tone at –90dBFS (fig.6), the noise floor dropped by 25dB, meaning that the DV2 offers 20 bits' worth of resolution, which is close to the state of the art. With undithered data representing a tone at exactly –90.31dBFS (fig.7), the three DC voltage levels described by the data were well resolved and the waveform was perfectly symmetrical. With undithered 24-bit data, the result was a superbly clean sinewave (fig.8).
Fig.6 EMM DV2, 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) (20dB/vertical div.).
Fig.7 EMM DV2, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).
Fig.8 EMM DV2, waveform of undithered 1kHz sinewave at –90.31dBFS, 24-bit data (left channel blue, right red).
Harmonic distortion was extremely low in level even into 600 ohms (fig.9), with the second harmonic the highest in level in the right channel (red trace), at –106dB (0.005%), and the third harmonic the highest in the left channel (blue), at –112dB (0.0025%). Intermodulation distortion was very low, with the second-order difference product produced by equal-level tones at 19 and 20kHz with the combined waveform peaking at 0dBFS, lying just below –90dB (0.003%) (fig.10). However, contradicting the spectra shown in fig.2 are several aliasing products visible in fig.10. Reducing the level of the test signal to –3dBFS didn't change this behavior.
Fig.9 EMM DV2, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 600 ohms (left channel blue, right red; linear frequency scale).
Fig.10 EMM DV2, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).
Tested for its rejection of word-clock jitter with 16-bit AES/EBU data, the DV2 turned in superb performance: all odd-order harmonics of the LSB-level, low-frequency squarewave were at the correct levels (fig.11, sloping green line), though with some broadening of the peak that represents the high-level tone at one-quarter the sample rate. This is presumably due to the presence of low-level, low-frequency random jitter components. There is also a pair of low-level, power-supply–related sidebands at ±120Hz. These sidebands and the spectral broadening were also present with 24-bit J-Test data (fig.12).
Fig.11 EMM DV2, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit AES/EBU data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.
Fig.12 EMM DV2, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 24-bit AES/EBU data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.
Overall, EMM Labs' DV2 offers state-of-the-art measured performance.—John Atkinson
Footnote 1: My thanks to Jürgen Reis of MBL for suggesting this test to me.
