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The second is a pentatonic (so-called black-note) cluster, indicated by the flat sign; a sharp sign would be required if the notes showing the limit of the cluster were spelled as sharps.
A chromatic cluster—black and white keys together—is shown in this method by a solid bar with no sign at all.
A tone cluster is a musical chord comprising at least three adjacent tones in a scale.
From the next century-and-a-half, a few more examples have been identified, mostly no more than a fleeting instance of the form, for example in the concluding two bars of the “Loure” from J. Bach’s French Suite No.5, BWV816: In the keyboard sonatas of Domenico Scarlatti (1685-1757), we find a more daring and idiosyncratic use of tone clusters.Blends them together and explains them to the ear." Tone clusters thus also lend themselves to use in a percussive manner.Historically, they were sometimes discussed with a hint of disdain.Prototypical tone clusters are chords of three or more adjacent notes on a chromatic scale, that is, three or more adjacent pitches each separated by only a semitone.Three-note stacks based on diatonic and pentatonic scales are also, strictly speaking, tone clusters.