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When Bach’s predecessors began to combine secular instruments with organs and voices in the performances of cantatas and passions, it was difficult to find pitch agreement among church and traveling musicians because organ pitches in Germany were, literally, all over the map. In comparison to today’s standard pitch of a’ = 440 Hz (“Hertz” or cycles per second), organs played as high as a’ = 487 (Buxtehude’s instrument at St. Mary Church in Lübeck) and as low as a’ = 416 (Silbermann’s organ at the Frauenkirche in Dresden), a range of about three half steps. In general, most German organs sounded around a’ = 466 (called “Chorton”), a half step higher than today’s orchestras. Even more strikingly, this Chorton was a whole step higher than the typical pitch (“Kammerton”) of most of Bach’s woodwinds.

While accomplished organists, such as Bach, could easily transpose their part in compensation for large tuning disparities, woodwind instruments and their players were less flexible. Their fingering system limited them to playing in keys with no more than a few sharps or flats, so professional woodwind players often carried two instruments, one pitched at Kammerton and another a half step lower, in order to play in more distant keys.

String instruments were also quite sensitive to the variability of pitch heights. When asked to tune up to match the organ or tune down to match the woodwinds, the responsiveness and tone of individual string instruments could change dramatically and unpredictably. As a result, the most mobile of string players in Bach’s time probably owned more than one instrument in order to accommodate both high and low pitch centers.

Therefore, whenever Bach was leading the performance of a cantata, someone was probably either selecting an alternate instrument or transposing their part. For example, vocal parts could be notated at either the Kammerton or Chorton standard, and when Bach was in Weimar, it was simpler for him to notate the voices with the organ and ask the strings to either tune high or transpose their part. In contrast, it was more common in Leipzig for Bach to write voice and string parts at Kammerton and ask the trumpets and organ to play their Chorton parts a whole step lower.

Bach was surely aware of the fact that the transposition of two or three half steps could have a disastrous effect on his singers. During composition, Bach would have carefully considered the tone qualities of the different vocal registers in order to avoid audible breaks from chest to head voice. Similarly, he would have guarded against an upward transposition that would transform a high tenor part into one for countertenor. It seems highly likely, then, that Bach had a reference pitch in mind.

Since the late nineteenth century, international agreements have encouraged orchestras to play at a’ = 440 Hz, but this pitch standard is generally considered too high for the performance of the works of Bach. As a result, the Boulder Bach Festival is adopting the Baroque Kammerton of a’ = 415 as its standard pitch. Performing Bach’s works at a lower pitch level more similar to his own will reveal new sonorities and enhance our understanding of Bach’s musical intentions.