The empty iv chord

The “empty” iv chord is a hip-hop producer’s technique: it’s when you play the iv chord without its third (the scale's ♭6).

Producers will voice chords without thirds, in general, because:

1. The normal place to voice the third, with a synth or a piano, is in the low- to mid-register
   • Why? If it’s too low, it’ll be muddy against the bass, and if it’s too high it sounds like a melody or countermelody line, and demands the ear’s attention
2. But when the 808 is playing the bass note, that range (200-400hz) is too crowded: 1) that’s where the rapper’s voice usually is and 2) that’s where the overtones of the 808 sound are strongest. And you don’t want to cover those up.
3. So producers take advantage of this limitation in a few ways:
   • Have implicit thirds, e.g. the melody hits the chord’s thirds.
   • Use both ♭3 and ♮3 in the melody
   • Avoid playing either a ♭3 or a ♮3

And you'll see this technique used in Phrygian Dominant sometimes.

The iv chord in Phrygian Dominant, if played as a seventh chord, is notated ivMaj7 - a minor-major seventh chord - and these types of chords usually sound intense due to the augmented triad they have internally. Many genres of music avoid augmented triads entirely. You'll notice this chord did not show up in any of the common vamp lessons.

So when the iv chord is used in Phrygian Dominant, it's almost always as a triad instead. If the seventh is played, it'll be played very subtly (grace note in the melody, etc.). Little hints of this intensity can be really interesting.

And it's extra interesting to drop the chord's third too.

iv can be a very tragic-sounding chord, and the tragic sound largley comes from the scale’s ♭6 (which is the chord’s third). Often we want a sound of power, oppression, etc. - but not sadness per se. So some ambiguity to make this a little more neutral-sounding is useful.

In practice this usually means just playing the scale's 4 in the 808 bass.