The Bach-Vivaldi Conversations are particularly interesting as they span a wide swathe of Bach’s career. First up, Bach’s transcription of Concerto No. 11 in D Minor for Organ.
Antonio Vivaldi, Concerto Op. 3, No. 11 in D Minor:
J.S. Bach, Organ Concerto in D Minor (After Vivaldi):
This is more or less a straight transcription. It is thought among some musicologists that Bach was commissioned to transcribe these for a patron; hence, the lack of invention. Or they were simply how Bach studied music—no one knows for sure either way. But here is a more mature Bach, in his Concerto for Four Harpsichords and Strings in A Minor, which is based on Vivaldi’s No. 10 for 4 violins in B minor. This is a true Conversation (seemingly composed for Gert with four harpsichords)—Bach takes a brilliant Vivaldi original to new heights, adding additional textures and harmonies. When Gert first asked for a list of great harpsichord works, this was the first piece I thought of.
Antonio Vivaldi, Concerto Op. 3, No. 10 in B Minor:
J.S. Bach, Concerto for Four Harpsichords and Strings in A Minor:
A Gertus History of Music 