I love Maurice Durufle's Prelude and Fugue on the name ALAIN, but I don't understand the mapping of the name "A-L-A-I-N" to the musical notes "A-D-A-A-F". Various websites such as https://www.allmusic.com/composition/prelude-and-fugue-on-the-name-alain-for-organ-op-7-mc0002363275 simply say that Durufle found an 'equivalent' for ALAIN in these notes. But I would like to understand the actual mapping, e.g. how Durufle came up with 'L' for the musical note 'D'.
It's a bit contrived, unlike BACH! To make it work, it needs ABCDEFGH, as used by German musos. If you write out ABCDEFGHABCDEFGH, and count letters further on than the first 8, you'll come to corresponding 'proper' note names, which are the ones used. It wouldn't work without the 'H'. Several other composers have used their own names as motifs, with greater (and lesser!) success.