Intonation is one of the most critical aspects of this style; florid lines require harmonic clarity which only good intonation can give. Nevertheless, intonation and tuning would themselves have varied with the performance context. When singers were unaccompanied, they would likely have sung simultaneous octaves, fifths, and thirds as close to pure as possible. But when they performed with instruments, we must assume that they adopted the instruments’ tuning. This is of particular concern with regard to the fretted strings and keyboard instruments, especially the organ, on continuo parts. Fretted strings such as lutes and viols can make some concessions to just intonation through the use of double fretting or variable finger placement and pressure at the frets, but keyboard instruments are completely inflexible, and any instruments or voices performing with them must match their pitches.
In the early seventeenth century, matching keyboard pitches often meant performing in quarter-comma meantone, which provides perfectly lovely pure thirds as long as one keeps to the right keys. By the time of Buxtehude, however, the use of a wide variety of well-tempered tunings were coming into vogue in Germany, especially the temperaments of Andreas Werckmeister. The greater chromatic flexibility permitted by these temperaments was balanced by the fact that more chords were slightly out of tune, although not as badly as the wolf chords of the meantone system.
In the early seventeenth century, matching keyboard pitches often meant performing in quarter-comma meantone, which provides perfectly lovely pure thirds as long as one keeps to the right keys. By the time of Buxtehude, however, the use of a wide variety of well-tempered tunings were coming into vogue in Germany, especially the temperaments of Andreas Werckmeister. The greater chromatic flexibility permitted by these temperaments was balanced by the fact that more chords were slightly out of tune, although not as badly as the wolf chords of the meantone system.