At this point in time, there are quite a few editions of W. Ferling's original 48 etudes. If IMSLP has served me well, there were no metronome markings in the original. Many oboists, however, use the Andraud edition, which does have metronome markings. The Marcel Mule edition has quite different metronome markings from the Andraud. Most of the slow etudes are marked at quarter = 72, which according to Dr. Eugene Rousseau, was Mule's favorite tempo for practicing vibrato. Mule also composed several additional etudes that cover all of the enharmonic keys up to C# and Cb. These are mostly very well done and almost indistinguishable in style from Ferling's. Dr. Rousseau has recently published his own edition of the slow etudes.
In my own journey with these etudes, I have approached them many different ways. Initially, it was a matter of learning the pieces, the notes, rhythms, ornaments, and phrasing. But as the years progressed I was able to go beyond most of the technical aspects. I found, at one time, that the most useful way to play them was without any vibrato at all. When I did this, I discovered how little I was actually doing with the phrasing. Be careful not to let vibrato become a musical crutch. It is a color with which we can shape our music, an ornament of the tone. The videos presented below (on YouTube by searching "Colin Lippy") represent my current thoughts on these pieces. While definitely inspired by Dr. Rousseau's instruction and the Mule edition, I no longer have much interest in one man's metronome markings. Rather, I am interesting in capturing the spirit of the music as best I can and in my own interpretation. They are no longer etudes for me but miniature works of art. I recorded them in a complete take with no editing or effects. The goal was to present them as realistically as possible, much as they are often played, in practice rooms or private lessons. I hope you enjoy these videos and find them useful in your own journey.
UPDATE: Be sure to check out Part 2: The Fast Ones.
Ferling 47/Mule 51