[20] Stanford Research Systems FS752 GNSSDO teardown, review, and experiments 

The phase noise performance of the FS752 is excellent, although it's an OCXO rather than something more exotic like a rubidium or cesium standard. What's your application? There's always a better clock, it just depends on your requirements and budget.

@@AndrewZonenberg I heard about the fs725 from srs which apparently is rubidium. That would be used for a digital clock with extreme low jitter for my ad and da converters ( audio mastering ) . I heard about microchip cesium csIII 4310B too

@@soundsokok You're not going to be clocking the ADC with the 10 MHz reference regardless, it's going to end up being fed into a PLL that generates the actual sampling frequency. Phase noise of the PLL VCO is going to dominate your final sampling clock jitter, much more so than the reference clock. And at audio frequencies, you don't need particularly stable clocks compared to what high speed digital applications demand. Linear Technology/Analog Devices has a nice appnote on this (DN1013, google it since YT doesn't like links in comments). With the example ADC and a 1 MHz signal (much higher than audio, so more sensitive) and 50ps of clock jitter (enormous by modern standards) you're still looking at a 70 dB SNR. Cut the clock jitter down to 10ps and the contribution from the clock is lost below the ADC's noise floor.

As a data point, the TI LMK0480x series PLL synthesizers use a dual loop architecture with an on-die VCO as the final stage, giving ~130fs RMS jitter IIRC. And they're specifically designed to clean up dirty clocks coming out of a CDR or similar and give you nice clean outputs for driving high speed ADCs. It would likely be perfectly happy eating the output of a cheap TCXO and generating a clock good enough for driving a GHz ADC, much less an audio ADC. (And there's likely cheaper options with worse performance that are still overkill for audio).

@@AndrewZonenbergright indeed ia reclocker would be needed to feed the converter bnc wordclock input . By snr you mean " signal noise ratio " ?