Sidebar 3: Measurements
I measured the Ideon Ayazi mk2 with my Audio Precision SYS2722 system. I performed the testing using the Ayazi's coaxial S/PDIF input, which accepted data sampled at all rates up to 192kHz, and its USB port. I repeated some of the tests feeding data to the 3R Master Time Black Star's USB port, the data then passed to the Ayazi's USB port. Apple's AudioMIDI utility revealed that the Ayazi's and Black Star's USB ports accepted 16- and 24-bit integer data sampled at all rates from 44.1kHz to 384kHz. Apple's USB Prober app identified both the Ideon products as "AYAZI True HD Audio\000" from "IDEON-AUDIO\000," with the vendor ID as "C-MEDIA ELECTRONICS INC." (C-Media Electronics is a Taiwanese computer hardware manufacturer.) The USB ports operated in the optimal isochronous asynchronous mode.
The Ideon's analog output preserved absolute polarity (ie, was noninverting), and the output level with full-scale 1kHz data was 1.975V, a negligible 0.11dB lower than the specified 2V. The output impedance was a low 234 ohms at 20Hz and 1kHz, 230 ohms at 20kHz.
The Ayazi's impulse response with 44.1kHz PCM data (fig.1) indicates that the reconstruction filter is a conventional linear-phase type, with symmetrical ringing before and after the single full-scale sample. With white noise sampled at 44.1kHz, the filter rolled off quickly above the audioband (fig.2, magenta and red traces), reaching full stop-band attenuation at 24kHz. The aliased image at 25kHz of a full-scale tone at 19.1kHz (cyan, blue) was therefore suppressed by more than 100dB. The harmonics associated with the 19.1kHz tone are all low in level, with the second harmonic the highest at just –80dB (0.01%).
Fig.1 Ideon Ayazi Mk2, impulse response (one sample at 0dBFS, 44.1kHz sampling, 4ms time window).
Fig.2 Ideon Ayazi Mk2, wideband spectrum of white noise at –4dBFS (left channel red, right magenta) and 19.1kHz tone at 0dBFS (left blue, right cyan) into 100k ohms with USB data sampled at 44.1kHz (20dB/vertical div.).
Fig.3 shows the Ideon's frequency response with S/PDIF data sampled at 44.1, 96, and 192kHz. The responses at all three sample rates follow the same basic shape: flat in the audioband with then a sharp rolloff just below half of each rate. Below 3kHz, channel separation (not shown) was excellent, at 99dB, R–L, and 108dB, R–L. It decreased to a still-excellent 94dB in both directions at the top of the audioband. The low-frequency noisefloor (fig.4) showed a power supply–related tone at 60Hz, but this was very low in level, at –110dB (0.0003%). The blue and red traces in this graph were taken with USB data. With S/ PDIF data (green and gray traces), there was a slight rise in the noisefloor close to the fundamental tone. The spectrum with USB data fed to the Black Star clock and then to the Ayazi was identical to the blue and red traces in fig.4.
Fig.3 Ideon Ayazi Mk2, frequency response at –12dBFS into 100k ohms with S/PDIF data sampled at: 44.1kHz (left channel green, right gray), 96kHz (left cyan, right magenta), and 192kHz (left blue, right red) (1dB/vertical div.).
Fig.4 Ideon Ayazi Mk2, spectrum with noise and spuriae of dithered 1kHz tone at 0dBFS with 24-bit USB data (left blue, right red) and 24-bit S/PDIF data (left green, right, gray) (20dB/vertical div.).
The Ayazi's linearity error with 24-bit data (not shown) was negligible until the signal lay below –120dBFS, which implies high resolution. An increase in bit depth from 16 to 24 with dithered data representing a 1kHz tone at –90dBFS (fig.5) dropped the Ayazi's noisefloor by 13dB, which suggests that the DAC's resolution is around 18 bits. The presence of the third, fifth, and seventh harmonics with 24-bit data (blue and red traces) suggests that the least-significant bit is being truncated. Repeating the spectral analysis with USB data with and without the external clock gave an identical result. When I played undithered data representing a tone at exactly –90.31dBFS, the three DC voltage levels were well-resolved (fig.6), though the symmetrical waveform was overlaid with high-frequency random noise.
Fig.5 Ideon Ayazi Mk2, spectrum with noise and spuriae of dithered 1kHz tone at –90dBFS with: 16-bit S/PDIF data (left channel cyan, right magenta), 24-bit S/PDIF data (left blue, right red) (20dB/vertical div.).
Fig.6 Ideon Ayazi Mk2, waveform of undithered 1kHz sinewave at –90.31dBFS, 16-bit data (left channel blue, right red).
Driving high impedances, the Ayazi produced very low levels of harmonic distortion. With a full-scale 50Hz tone, the second harmonic was the highest in level in the right channel, at just –90dB (0.003%, fig.7). The third harmonic lay at –94dB (0.002%) in both channels. With the Ideon DAC driving the punishing 600 ohm load, the distortion increased dramatically (not shown), unless I reduced the signal level by 6dB. The Ayazi should not be used with preamplifiers that have an input impedance below 1k ohms. Intermodulation distortion with an equal mix of 19 and 20kHz tones, each lying at –6dBFS and sampled at 44.1kHz, was very low in level into high impedances (fig.8).
Fig.7 Ideon Ayazi Mk2, 24-bit S/PDIF data, spectrum of 50Hz sinewave, DC–1kHz, at 0dBFS into 100k ohms (left channel blue, right red; linear frequency scale).
Fig.8 Ideon Ayazi Mk2, 24-bit S/PDIF data, HF intermodulation spectrum, DC–30kHz, 19+20kHz at 0dBFS into 100k ohms, 44.1kHz data (left channel blue, right red; linear frequency scale).
Fig.9 shows the spectrum of the Ayazi's output when it was fed high-level, 16-bit J-Test data via S/PDIF. The odd-order harmonics of the undithered low-frequency, LSB-level squarewave lie at the correct levels, indicated by the sloping green line, though a trio of low-level spurious tones is present between 8kHz and 10kHz. These tones disappeared when I repeated the analysis with 16-bit J-Test data sourced via USB (fig.10), though a pair of low-level sidebands at ±120Hz was now present. I ran the test again with a wire connecting the Ayazi's ground to the analyzer's chassis ground; the sidebands were still present, as they were when I performed the spectral analysis by feeding USB data to the external Black Star clock then to the Ayazi.
Fig.9 Ideon Ayazi Mk2, 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 (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.
Fig.10 Ideon Ayazi Mk2, high-resolution jitter spectrum of analog output signal, 11.025kHz at –6dBFS, sampled at 44.1kHz with LSB toggled at 229Hz: 16-bit USB data (left channel blue, right red). Center frequency of trace, 11.025kHz; frequency range, ±3.5kHz.
Overall, Ideon's Ayazi did well on the test bench. I didn't find any difference in its performance when fed USB data directly or via the 3R Master Time Black Star.—John Atkinson
