The Notation of Polyphonic Music 900-1600, by Willi Apel
Essays in Musicology
Gregorian Chant, by Willi Apel
Gregorian Chant
Neapoletan Links Between Cabezon and Frescobaldi, by Willi Apel
French Secular Music of the Late Fourteenth Century Ed. by Willi Apel. D. of the Literary Texts by Robert W. Linker and Urban T. Holmes, Jr.,....
Willi Apel. Geschichte der Orgel- und Klaviermusik bis 1700
Medieval Music
The Apel Collection of Early Keyboard Sources
The Harvard Brief Dictionary of Music by Willie Apel
Early European Keyboard Music
The Apel Collection of Early Keyboard Sources ...
Harvard Dictionary of Music
Remarks about the Isorhythmic Motet
The Apel Collection of Early Keyboard Sources
La notation de la musique polyphonique 900-1600
Historical Anthology of Music: Oriental, medieval and Renaissance music
Die spanische Orgelmusik vor Cabanilles