Popular Post JohnSwenson Posted June 4, 2017 Popular Post Share Posted June 4, 2017 As Alex mentioned I will soon have test equipment to do accurate phase noise measurements of very low phase noise clock systems, and thus be able to actually measure DAC clocks in system while playing music. The measurements of analog out from DACs is a much harder concept. Remeber we are trying to measure the difference on an analog waveform due to very small jitter differences. You can't just do this with a $200 ADC and an FFT. It takes a high resolution ADC with a clock system that has a jitter level significantly lower than what you are trying to measure. To get decent resolution in the output the FFT needs to be done over a very long time, over which the reference clock is not wandering, which will mess up the results. The APs are not even close to being able to do this. I don't know of ANY existing test equipment that can do this. The test @jabbr mentioned, playing a pure tone through the DAC and doing a spectrum and looking at changes in the "skirt" is probably a very good way to test this, but with existing test gear the skirt from the test equipment is going to be wider than what you are trying to see, again not a particularly useful test. It seems to me that the most promising measurement system is to use a cross correlation phase noise system that has been designed to work at audio frequencies. This at least theoretically has the resolution to distinguish differences in the audio out due to jitter changes in a good DAC, but nobody has built one. That will have to be something else I look into building. So "just sending it out to a third party to measure" is not going to be a particularly useful test, since nobody else has any test equipment that is going to be able to measure the effects that the ISO REGEN is designed to produce. Of course they can measure unrelated things like noise floor, but that is not the same as measuring jitter effects in the range we are addressing. John S. PeterSt, Keith_W, christopher3393 and 2 others 5 Link to comment
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