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AK4493 in oct/hex mode - oversampling filter bug?



Please does anyone have a practical experience with AK4493 in oct or hex sampling speeds, i.e. 384+kHz sample rates?

When MCLK is at least 128xFS and sampling speed (DFS0-2) at most quad, the DAC outputs correctly oversampled signal. When dropping MCLK to 96xFS and setting corresponding sampling speed to oct or hex, the DAC output waveform is broken.

This is 96kHz sine generated at 384kHz. The chip officially supports MCLK 49MHz, hence I can set MCLK=128xFS and the corresponding quad sampling speed. The output waveform is flawless:


and detail showing the oversampled steps:


However, when using MCLK = 96xFS (correct ratio according to the datasheet http://d.zaix.ru/5cHC.pdf ) and the corresponding oct sampling speed, the DAC output waveform is broken:



The same occurs for the hex sampling speed (e.g. at 768kHz or even at 384kHz with MCLK = 64xFS). I am surprised nobody would have noticed such a weird behavior, but have not found anything being discussed about this. Well I have not found any technical discussion of using these chips at fs > 192kHz (but they are used in commercial soundcards supporting up to 768kHz).

Thank you very much for any hints and recommendations.



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