Interval

How intervals are named

The name counts the degrees the distance spans, counting from the first to the second tone inclusive. From C to E there are three degrees, so it is a third. The size is stated more precisely with the addition major, minor, perfect, diminished or augmented. Unison, fourth, fifth and octave are called “perfect”; seconds, thirds, sixths and sevenths come in a major and a minor form.

The just ratios apply to beat-free tuning. The piano uses equal temperament, in which all semitones are the same size and only the octave is pure. The frequencies on the piano and the guitar therefore deviate minimally from the just values.

What you hear

The simpler the ratio of the frequencies, the more fused two tones sound together. The octave (2:1) and the fifth (3:2) sound most stable, the tritone the least decided. Consonance is therefore a matter of numerical ratios, as the article Why the fifth sounds hollow explains.

You also distinguish the direction: ascending is the normal case and the most important at the start. Descending has to be practised separately, because a descending interval does not sound like a reversed ascending one. With a harmonic interval both tones sound at the same time; here you hear the colour of the combined sound, and that is a skill of its own.

Intervals build chords

If you stack thirds on top of each other, triads arise: major from a major and a minor third, minor from a minor and a major one. The fifth between the outer tones is perfect in major and minor.

Common mistakes

• Mixing up semitones and degrees: The fifth has seven semitones but spans five degrees.
• Starting with too many intervals: If you practise all twelve at once, you guess and remember nothing.
• Practising only upwards: Descending intervals sound different to the ear and need their own training.