Bach Trio Sonata for treble recorder, treble viol and harpsichord, played by The Herschel* Trio. This piece begins at 48:17.
This is a transcription of one of my absolute favourite pieces of music - the Vivace (first movement) from JS Bach's G Major Trio Sonata for Organ BWV 530. The whole thing is pure delight - but the three extended descending sequences are so absolutely delicious as to bring tears to the eyes. (The first of these begins at 49:09).
In the first version of this sequence the recorder does rapid semi-quavers while the viol does triplet quavers in syncopated support with the bass note coming on the first beat. The second sequence switches the lines with triplets in the recorder and semi-quavers on the viol. And the third sequence has both recorder and viol playing semi-quavers in mirror movement, with the bass note coming on the third ('off') beat.
If you want to take a look at how the music 'works' - then the first part of this scrolling version of the original organ piece is very useful.
If you want to watch the music being played (especially the bass line - articulated in beige socks...) then try this one: