I noticed two different problems on Najda used with FIRs, or more precisely when the DSP performs a lot of computation or above 50% activity on the 2 coprocessors.
problem 1: random phase shift between channels with FIR files having the same samples.
problem 2: distortions in the upper midrange / treble perfectly audible, which appears after several switching on and off of Najda, without ever modifying anything in the configuration of the filters ... This distortion can disappear by "magic" after a change of filter file in the NUC ...
These problems appear on the basic version of NAJDA with FIRs, and also continue in I2S input and output use, so the only common active element remains the DSP, which must be the source of the problems, when it manages a very large amount of calculation.
The power regulators do not seem to me to be the cause, Nicolas very well decoupled the various active circuits of Najda, and perfectly separated the masses of the digital and analog stages. I know these problems quite well because I come from the world of Radio-Frequencies.
I think these are issues related to the computing power installed in the DSP, and how to deal with it with software (I'm not a developer!) Which creates random instabilities.
Despite everything, it is undeniable that Najda remains a very interesting solution for lucky DIY enthusiasts, who are lucky enough to still own one or more, because it is possible to experiment a lot, there is a replacement for the " great "Precision Analogue solution, but it is not the same budget!