He posits that Bach avoided F#6 in BWV 1049, at the cost of inferior counterpoint, reinstating them as E6 in BWV 1057. In the second movement, breaking of beaming in the parts, markings of f and p, the fermata over the final double bar of the first movement, and the 21 bars of rest at the beginning of the third have led some musicologists to argue that Bach intended the use of "echo flutes" distinct from normal recorders in the second movement in particular. The breaking of beaming could be an indication of changes in register or tonal quality, the rests introduced to allow the players time to change instruments, and the markings of f and p further indicative of register or sound changes. Marissen has demonstrated that the f and p markings probably indicated tutti and solo sections rather than loud and soft ones. A number of instruments other than normal recorders have been suggested for the . One of the earliest proposed alternatives, by Thurston Dart, was the use of double flageolets, a suggestion since revealed to be founded on unsteady musicological grounds. Dart did, however, bring to light numerous newspaper references to Paisible's performance on an "echo flute" between 1713 and 1718. Another contemporary reference to the "echo flute" is in Etienne Loulié's (Amsterdan, 1696): (The sounds of two echo flutes are different, because one is strong and the other is weak). Loulié is unclear on why one would need two echo flutes to play strongly and weakly, and on why it is that echo flutes differ. Perhaps the echo flute was composed in two halves: one which plays strongly, the other weakly? On this we can only speculate. Surviving instruments which are candidates for echo flutes include an instrument in Leipzig which consists of two recorders of different tonal characteristics joined at the head and footjoints by brass flanges. There is also evidence of double recorders tuned in thirds, but these are not candidates for the parts in BWV 1049. "" RV 443, 444, 445 Vivaldi wrote three concertos for the , possibly for performance by students at the Ospedale della Pietà in Venice, where he taught and composed in the early eighteenth century. They feature virtuosic solo writing, and along with his concerto RV 441 and trio sonata RV 86 are his most virtuosic recorder works. They each survive a single hastily written manuscript copy,