Trills in a Barque Piece

[dorothy]

I am learning John Blow's Prelude in C Major.  In the third measure, there two sets of half notees, one on top of the other.  The second group, a b and d, has a trill over it.  How does one go about a trill with two notes.  I can't find any information anywhere about this.  I have listened to several different people perform this piece, and there is a trill there, so it is not a misprint, but it is too fast to see where their fingers are going.  Can someone answer this?  Thank you!

[anacrusis]

Hello and welcome to Piano Street!

I'm looking at this score https://ks4.imslp.net/files/imglnks/usimg/d/d8/IMSLP125901-WIMA.e4ae-Blow_Prelude_C.pdf, is it the right piece?

As it is notated in that file, the trill is understood to only apply to the top note. If he had wanted a trill on the bottom note, the sign would have been under it. If he had wanted a trill on both notes, there would be a trill sign on both.

[dorothy]

Yes, this is correct piece.  So, would I trill d-e, d-e, d-e before hitting the b underneath or hitting the b when the trill begins?  This is probably elementary, but it's confusing to me.  I appreciate  your help. 

[anacrusis]

You hit the b when the trill begins. In Baroque music, the trill often starts on the upper note, so you may play it as e-d e-d e-d instead if you want. But the b goes together with the first note of the trill in this case.

[dorothy]

Thank you.  This is exactly what I wanted to know.  I will start practicing it this way.