The New Grove Dictionary of Music and Musicians, 2nd edition

The New Grove Dictionary is the standard reference work for music history, with named specialist contributors writing individual entries under editorial oversight, and this atlas cites it specifically for its entries on Guido of Arezzo, the hymn Ut queant laxis and solmisation as a system of relative rather than absolute pitch. That specialist, entry-by-entry authorship under documented editorial review is the dictionary's real evidentiary basis rather than a claim resting on its long publishing history alone. This record has not independently traced further scholarly disagreement with any specific entry since this second edition. Use it for established musicological facts about a specific topic a named entry addresses; a claim about a modern popular music theory, such as the Solfeggio frequency movement's own claims, needs a separate source addressing that specific modern claim.