HPR1754: D7? Why Seven?

In this episode I respond to one of the community-requested topics ("Music Theory") and try to explain what seventh chords are and why they are used. Below are some of the terms that I use in the course of the discussion.

• Interval: The distance between two pitches (sounded either consecutively or simultaneously)
• Consonance: Relatively stable sound between two or more pitches
• Dissonance: Relatively unstable sound between two or more pitches. Dissonance often needs a "resolution" to consonance
• Chord: three or more notes sounded together
• Chord progression: a succession of chords
• Triad: a chord with 3 pitches, the adjacent pitches separated by the interval of the 3rd.
• Seventh chord: a chord with 4 pitches, the adjacent pitches separated by the interval of the 3rd.
• Tonality: harmonic system that governs the use of major and minor keys
• Tonic: the central tone of a piece of music
• Mode: major or minor [e.g. Symphony no. 5 in C minor]
• Modulation: the process of changing keys within a piece of music
• Scale: Ascending or descending series of notes that define a key or tonality, with a specific arrangements of half-steps and whole-steps. Major and Minor scales are most common in Western music

Free public-domain music reference book: Music Notation and Terminology by Karl Wilson Gehrkens: https://www.gutenberg.org/ebooks/19499 (see ch. 18)

Free Online Music Dictionary: https://dictionary.onmusic.org/

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