Nicola is right to say anyway is fine as long as it it consistent.
TBH, I wish we had taught several pips for recall as there is more chance of the whistle being heard if the dog is a little way from you,we only taught two short pips.
We still need to teach a stop whistle but we are having a few problems at the moment as OH has been doing his own thing with the whistle and has over used it especially when he is annoyed and blasts the whistle till red in the face,she doesn't get what she is supposed to do when he does this,
So my advice would be what ever you do,consistency is the key
As for pips for turning,i need to train OH first.....