B♭ dominant 7th chord

What each note does

• B♭ is the root. It names the chord and is the note your ear hears as home.
• D is the major third. It makes the chord sound bright. Lower it a half step to D♭ and the chord turns minor.
• F is the fifth. It adds weight without changing the character, so it is the first note to drop when a voicing gets crowded.
• A♭ is the flat seventh. It adds tension that pulls toward the chord a fourth above, the sound of blues and of a V chord heading home.