Observable data: seasonal adjustment first or log difference first

Dear Johannes,
Could I ask a simple question, when do data transformation for observable variables of DSGE models, should we do seasonal adjustment prior to log difference of data, or should we do log difference prior to seasonal adjustment?
Thank you very much and look forward to hearing from you.
PhD Candidate

I would apply the seasonal adjustment to each series individually. After all, the seasonal patter is in the data before any transformations.

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