Not one, but two prominent musicians of the Baroque era discussing the finer points of vocal performance practice of that period, plus valuable clarifications and cross-references provided by a modern scholar (Baird). So many aspects of Baroque vocal performance practice were never written down by the composers - it was expected that the performers would improvise ornamentation in the style of the day. Consequently, rare sources like this one provide the modern scholar with some of the only available primary source material on the subject. Well-organized and surprisingly easy to read.