3.9-4 is way to little acidity for my palate, 3.4 sounds much better IMO. I'll add malic acid right before bottling the cider if the apple blend didn't add enough naturally but it's about taste, not to achieve a pH.
Never heard of anyone raising the pH of cider intentionally, since the acidity is such a defining characteristic when it comes to American ciders. I'm sure someone has though.
In all the states no door stands wider,
To ask you in to drink hard cider