The chug is a hand doing the work a gate plugin gets credit for.

A vibrating guitar string is a simple physical system — its pitch depends on length, tension and mass per unit length, and its overtone content depends on how freely it’s allowed to keep vibrating. Resting the edge of the picking-hand palm against the string doesn’t change its length or tuning; it changes how much energy that vibration is allowed to hold onto. The palm acts as a damper, absorbing energy out of the string with every cycle, which shortens sustain and — because higher overtones lose energy faster under damping than the fundamental does — leaves a note that reads as thicker and lower even though its actual pitch hasn’t moved.

That’s the physical basis for why a palm-muted note doesn’t just sound quieter than an open one — it sounds different in character: shorter, denser, with less of the ringing overtone content that gives an unmuted note its shimmer.

Pressure is the second variable, and it’s continuous rather than binary. A light touch produces a subtly muted tone — still pitched, still has some sustain, just tamed. Heavy pressure pushes the technique to its percussive extreme: the “chug” heavy music leans on constantly, where the note is barely pitched at all and reads mostly as a rhythmic thump. Sweetwater’s technique guide describes this range plainly — light pressure gives a slightly muted sound, heavy pressure delivers close to pure percussion — and most heavy-guitar playing lives somewhere between those two poles, adjusting pressure moment to moment for the part.

Picking-hand dynamics interact with all of this. Strumming or picking harder while holding the same palm pressure pushes more energy into the string before the damping absorbs it, which is how a player controls the chug’s loudness and bite without ever moving the muting hand itself.