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ADAU 1701 - Is there an Advantage of using a 24,576 MHz Crystal than a 12,288 MHz Crystal? Is there a different noise result?

Hi there, 

I'm new to the Support Community and I hope that I write in the correct Place. 

I have an ADAU1701 Evaluation Board and would like to know what the advantage is of using a 24,576 MHz Crystal vs. a 12,288Mhz Crystal? Is there an advantage for one of the Frequencys? I have read many different Questions and FAQs but didn't find a hint why someone would use one over the other. 

I would also like to know if there is a difference in terms of noise? 

Thanks in Advance from Germany

Greetings

Anton

  • Hello AMueller,

    As you might notice, we tend to use a 12.288MHz crystal in all of our eval boards. This is the default values for the PLL in the parts. 

    The big difference you will see by using a higher frequency is that the PLL will lock faster. You can argue that the PLL will be more stable and more accurate when tracking a higher frequency. If the frequency of the PLL output verses the input begins to drift the correction will happen sooner and be a less severe correction. However, both are rather high frequencies so I would not expect a big difference in the jitter performance and I think it would be difficult to actually hear the difference in the audio. 

    I would like to hear from anyone who has done listening tests on this subject and if the tests were double blind it would be really good. 

    Jitter measurements would also be interesting but we have not done a good study of this here in the lab. 

    I do want to mention that with the ADAU1761 I have seen an issue where the PLL will not lock to a 24.576MHz MCLK about 1 out of 4 attempts when using the settings in the datasheet. The solution is to engage the input divider to divide it by 2 then set the PLL to the same as you would with a 12.288MHz clock. With the 1701 I have not seen any issues.  

    Dave T