Wednesday, November 12, 2014

ODAC Measurements

These measurements were made with an EMU0404, The tests are indicative of the ODAC's performance on a good day. The ODAC as suspected test really well, these are single channel test with the right channel of the ODAC testing worse than the left(0.003% vs 0.00068%) As expected the performance is resonable however due to the nature of Sabre based devices, we get noise floor with plenty of spuriae.

Fig 1.
Low level resolution of a 1khz tone @-90.31dbFS, as expected, not free of spuriae. 

Fig 2.

Fig 3 shows the Dunn Jitter Test of the ODAC on a good day/time where the ODAC sounds clean and reasonably transparent. In the worst case scenario, this jitter sidebands. rises to -115dbFS with a lot more sidebands. While arguably inaudible, to me the changes were so significant you practically have to be deaf not to hear it. A usb reset by plugging in and out does the trick but a device like the Wyrd helps the clock maintain good lock on the data stream.

Fig 3.

Adding a usb decrapfier or linear power supply helps with increasing the ODAC's performance as shown in Fig 3a.

Last of all, a test showing the reconstruction filter of the ODAC. This test is made by playing a full scale 19.1khz tone and white noise in 44.1khz sample rate to test the ODAC's reconstruction/anti-aliasing filter. This is then captured by the EMU0404's ADC at 192khz to observe the ultrasonic behavior of the device under test. An aliasing product at 25khz will be observed due to the mathematical implications of using a 19.1khz tone which nears the 22.05khz border of the bandwidth of the sampling frequency at 44.1khz. 


The odac seems to use quite a strong linear phase filter going by the sharp rolloff of 44.1khz white noise. Suppression of the aliasing product at 25khz is very strong at ~ -118dbFS However, the ultrasonic harmonics of the 19.1khz go on outside the audio band and at pretty significant levels.

Fig 4.
 Subjectively, I thought the ODAC is an okay DAC at most given its current price point. There are more consistent sounding DACs from the same price point to be had like the UD120 from Stoner Acoustics. The Geek products would be a better choice for a Sabre sound these days given what trusted ears say about them. A problem I think is that the Sabre tonality gets to me over a long period of time and while I like the clean transients, I found it too tonally lean and fatiguing over time which is probably cause by the measured spuraie. The EMU0404 I have tops out as the better sounding interface.

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