The notes D# and Eb are said to be enharmonic. They are the same note on an instrument but not in the study of intervals. The interval of zero steps, i.e. D#-D#, is called a unison, but this spelling, D#-Eb, could be called a diminished second (-2).

Consider these notes three 1/2-steps apart. The interval from C to D# is an augmented second (+2). The interval from C to Eb is a minor third (m3). Spelling counts!

Here are some examples of enharmonic intervals.

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