ProAudio Review - October 2008 - (Page 37) STUDIO | BENCH TEST rates of 44.1 & 96.0 kHz and at about –137 dBFS at the 192.0 kHz sample rate. These data PRISM BENCH TEST Continued From Page 19 between channels is in the D/A converter. In a final test of the D/A converter, a 500 Hz sine wave jitter at 1 UI (Unit interval) was imposed on the 1 kHz 0 dBFS digital test signal output to see the effect of this in the distortion of the converted audio. As in just a few of the D/A converters that I have made this test on, the Orpheus completely rejected the effects of the added jitter, which would show up as strong sidebands at 500 and 1500 Hz, as shown plotted in Figure 8. D/D performance When I first started looking into the D/D behavior of the Orhpeus, I discovered that the SNR was nowhere near the expected threshold of the Audio Precision, which is usually around –140 dBFS at the 44.1 & 96.0 kHz sample rates. This equates to about 23 bits of resolution. It was more like 106 dBFS. That is when I figured out that unused channels that were not muted were contributing noise to the FireWire buss. Muting all unused channels pretty much got the D/D noise levels down to the Audio Fig. 7 A/D THD+N as a function of decreasing signal level and measurement bandwidth at a sample rate of 192.0 kHz. Red/Blue = Ch 1/Ch2 at 22 kHz measurement BW, Magenta/Cyan = Ch1/Ch2 at 80 kHz measurement BW. Precision threshold. This obviously affected the other modes and all measurements on them and the D/D mode were with only channels 1 & 2 active with all others muted. Needless to say, the D/D frequency response was dead flat right out to the Audio Precision generator limit at each sample rate. THD+N vs. frequency and sample rate was at –140 dBFS from 20 Hz – 20 kHz for sample Fig. 8 D/A THD+N mode spectrum of 1 UI 500 Hz added jitter to 0 dBFS 1 kHz digital test signal with the measurement bandwidth set at Fs/2. Signal to noise ratios, dynamic ranges, and quantization noises were all essentially down to Audio Precision Thresholds. Finally channel separation was generally better than 150 dB with a few strange anomalous peaks at lower frequencies that reached –140 dBFS. — Bascom H. King August 30, 2008 Deep, Dimensional Sound Introducing The Wedge Versatile large-diaphragm studio condenser mic Wedge shape effectively reduces plosive sounds and wind/pop/breath noises Innovative free-standing design results in more open, detailed sound from any angle First stage circuit is located close to the capsule for improved sound quality violetusa.com www.proaudioreview.com October 2008 | ProAudio Review | 37 http://www.violetusa.com http://www.proaudioreview.com
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