The Minor 7th

10 semitones — blues & dominant sound

Prove it — just do the practice exercise.
C → Bb 10 semitones
C (root) Bb (♭7)
The minor 7th (♭7) = 10 semitones:

• In Dom7 and m7 chords
• Gives the chord "color" and depth
• Together with a major 3rd → dominant tension
• Together with a minor 3rd → minor character

Example: C → Bb = minor 7th

The minor 7th is THE jazz interval.