Equal termerament, as we know it today, did not exist in practice or literature, until about 1917 (twentyth century). What Bach used was most decidedly NOT equal but was Well Termerament in which most, but not all, fourths and fifths are tuned pure. Keys of F G and especially C are very pure and sweet whereas, the respective sharp signature are disonenet and harsh. Bach's twenty four preludes and fagues was written to explore the tonalities of untempered intervals. More later if you want it. Newton nhunt@rci.rutgers.edu
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