DAC - Jitter Tests

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Test Methodology:

There are a variety ways of measuring jitter but the single single RMS or peak jitter metric is not very revealing since it does not reveal the nature of the jitter, so a more detailed analysis such as the J-test method is used to test the susceptibility and tolerance of the device under test. The J-test methodology is described on the ASR forum J-test methodology 1 and J-test methodology 2

Test Results:

• J-test SPDIF input (Direct DAC mode)
• J-test Toslink input (Direct DAC mode)
• J-test USB input (Direct DAC mode)
• J-test dScope III internal generator test
• J-test S/PDIF Input (Preamplifier mode using the SHARC ASRC)
• J-test S/PDIF Input 16-bit (Direct DAC mode)

Conclusion:

As one can see from the detailed spectra in the following tests any side bands from the J-test are buried way into the noise floor below the threshold of hearing and should not pose any audible issues at all ! In fact, because all three test results are very similar it is possible that we are measuring the jitter of the analyzer itself !! All in all an exceptional result and shows the effectiveness of the high quality oscillator used, the clock distribution network, the jitter reduction hardware in the Sabre DAC as well as the careful attention to detail that we placed in the design of the DAC and pcb layout

Compared with the DEQX Pre-mate as measured by Stereophile we can see that the Ultimate-Preamplifier indeed has way superior jitter performance

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Nothing to see here !! Vanishing levels of jitter artifacts all way below the threshold of hearing. A truly impressive result !

J-test S/PDIF input with expanded frequency scale - we see a very clean spectrum with some very minor side-bands all way below the threshold of hearing !

To put these results into perspective it is useful to compare to other Sabre DAC designs such as the Benchmark DAC3 considered to be defacto reference in the industry. From the review of the Benchmark DAC3 on the ASR website we can see that the Ultimate Preamplifier displays lower sideband components and very similar noise floor compared to the Benchmark-3 DAC (once the reference levels are taken into account)



Compared with Okto DAC the Coax S/PDIF interface on the Ultimate Preamplifier exhibits much less jitter

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Nothing to see here either. Everything is way below the threshold of hearing and buried among the noise floor !!

J-test Toslink input with expanded frequency scale

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And the USB interface is pretty much on par with the other two tests using S/PDIF source

J-test USB input with expanded frequency scale

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Some additional spikes here, In terms of jitter the analog generator in the dScope III is not as good as the ES9038PRO Sabre DAC in the Preamp

J-test dScope III internal generator test with expanded frequency scale

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In this test we are looking at the jitter performance of the Asynchronous Sample Rate Converter built into the SHARC DSP which is used in the 2 or 8 Channel Preamplifier modes. There is more sideband noise compared to the other direct DAC tests but since it is random in nature it should not be objectionable at the levels measured !

Expanded frequency scale

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In this test we reduced the resolution from 24 bit to Red-book 16 bit standard and observe the resulting spectrum which we can see is still very clean with any of the artifacts still below the threshold  of hearing.

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Compare with the DEQX Pre-mate as reviewed by Stereophile we can see that the DEQX needs a lot of work to match the outstanding performance of the Ultimate Preamplifier even for Red-Book 16 bit playback