Logical problem with CTF 3rd order gradiometers correction

[Cristiano Micheli]

About point 2 and 3 of Michael's email
Is it unimportant if I apply denoise_synthetic before or after preprocessing?
I thought denoise_synthetic applies a non linear transformation of the data
so that any filtering preprocessing should be done immediately after this.
If this is the case i propose the following schema:

1) 'read-in' preprocessing: simply reads the dataset in a structure without
doing anything
2) denoise_synthetic
3) filtering

In code:
1)
cfg = [];
cfg.dataset    = 'Mydata.ds';
cfg.datatype   = 'continuous';
cfg.channel    = 'all'; 
cfg.trl = 'Mytrialfunction';
cfg.headerformat = 'ctf_new';
cfg.dataformat    = 'ctf_new';
meg = preprocessing(cfg);

2)
cfg = [];
cfg.gradient = 'G3BR';
cfg.trials   = 'all';
meg_d  = denoise_synthetic(cfg, meg);

3)
cfg = [];
cfg.channel = 'MEG';
cfg.hpfilter  = 'yes';
cfg.hpfreq   = 1;
meg_df = preprocessing(cfg, megd);

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