Sidechain Ducking
Invert the envelope and one sound pushes another out of the way - the pumping feel of modern pop/EDM.
Envelope Inversion
An envelope follower tracks how loud a signal is over time. Normally you'd use that to open a filter or trigger something. But flip it upside down and you get something different: when the first sound gets loud, the second sound gets quiet.
That's sidechain ducking. A kick drum triggers an envelope. The envelope gets inverted and applied to a pad. Every kick hit squashes the pad, and the pad swells back up between hits. That rhythmic pumping is all over EDM, French house, and modern pop.
How It Works
The kick plays through to the output normally. A copy of the kick also feeds an envelope follower that tracks its loudness. That envelope gets flipped (subtracted from 1) and scaled by the duck depth. The result controls the pad's volume:
pad volume = 1 - (kick envelope x depth)
When the kick hits, the envelope jumps to 1 and the pad drops. As the kick decays, the pad recovers. The release time controls how fast the pad comes back.
Try it - press Play and listen to the pumping effect. Toggle ducking on and off to hear the difference. Crank the depth to 100% for the full EDM experience, or dial it back for subtle movement.
Why It Matters
Sidechain ducking is a mixing tool. In a dense mix, the kick and bass compete for the same low frequencies. Ducking the bass on every kick hit gives each one its own moment, even though they sit in the same frequency range. This is why EDM bass lines sound impossibly loud: they're only loud when the kick isn't playing.
Same technique works for vocals over music, narration over ambience, or any time two sounds fight for space. Radio DJs, podcast editors, and film mixers all use it constantly.