Chromatic fourth in Johann Sebastian Bach's Well-Tempered Clavier (the chromatic fourth is indicated by a red bracket). From Fugue No. 2 in D minor of the second book of Bach's Well-Tempered Clavier (BWV 875). Entered into Finale 2006, with red bracket added in Photoshop. The music this excerpt comes from is public domain. My selection and addition of bracket is GFDL.
Author: The original uploader was Hyacinth at English Wikipedia.