Augmented unison

The augmented unison (A1) is an enharmonic interval that spans 1 semitone. It sounds like a minor second, but its spelling indicates an altered unison with specific theoretical meaning.

Construction and spelling

A1 is written as the same letter raised chromatically, such as C-C# or F-F#. Unlike m2, both notes keep the same letter name. This spelling is used when harmonic function requires altered scale-degree interpretation.

Harmonic and melodic usage

In practical music, A1 appears mostly in notation-driven contexts: chromatic voice-leading, altered lines, and theoretical analysis. Sonically, it behaves like a semitone, but structurally it marks alteration of a single pitch class. It is especially useful in advanced tonal and post-tonal spelling.

Examples

• Chromatic raising of a scale degree within one letter name
• Analytical contexts distinguishing A1 from m2
• Notated altered tones in functional harmony exercises

In practice

Train A1 by reading and writing interval spellings, then compare C-C# with C-D♭ to hear same pitch distance but different function labels. Combining ear and notation work helps internalize enharmonic logic. Strong A1 understanding improves theoretical accuracy in analysis and composition.