Put a free-running auto-pan on a shaker and it usually sounds wrong within two bars. The part is rhythmic and the motion is not. The pan drifts across the beat, so one hit lands left, the next lands slightly less left, and the movement reads as a wobble laid over the groove rather than part of it.
There are two ways to fix that. Lock the motion to the bar line, so a lap of the pan lands where the bar does. Or stop treating the motion as a continuous sweep and move the part only when it plays. This post covers both, using Locomotion, a 3D auto-panner with host sync and a trigger mode built for exactly this.
Why percussion needs the motion locked to the grid
A pad hides the shape of an auto-pan: the sound is always there, so you hear a smooth glide. Percussion is the opposite. A hi-hat, a shaker or a tambourine is a string of short events with silence between them. You do not hear the pan move. You hear a series of positions, one per hit, sampled wherever the sweep happens to be when each hit arrives. If the sweep rate has no relationship to the tempo, those positions never repeat, and the pattern of left and right falls out of step with the pattern of the playing. The ear reads that as untidy, because it is.
So the first job is to make the lap a musical length.
SPEED in Locomotion runs free from 0.02 to 20 Hz, or locks to the host's bar line from 8 bars down to 1/32. With TEMPO SYNC on, the lap is read off the host's bar position, sample-accurate. That has two practical consequences. It survives loops and transport jumps, so starting playback halfway through a chorus puts the image where it would have been anyway. And two instances never drift, so a shaker on one track and a tambourine on another can share a lap length and stay in a fixed relationship to each other for the whole song.
START sets where on the path a lap begins. On a percussion part that matters: it decides whether the downbeat lands left, right or centre. TAP TEMPO sets the lap to a tapped interval instead; it takes SYNC off, so use it when you want a rate that is not a bar division.
PATH picks the route. CLASSIC is side to side. BOUNCE is hard left and right, which on percussion gives the clearest alternation because there is no in-between for a hit to land on. CIRCLE, FIGURE 8, ORBIT and RANDOM are there as well. The store's own suggestion for a rhythm part is BOUNCE or CLASSIC locked to a bar, with FEEL toward RUSH: the old stage trick, without the level dip.
FEEL runs from RUSH to DRAG. It swings the lap or holds every other move back, which is the difference between a pan that moves like a metronome and one that leans into the beat the way the player does.
Moving on hits: TRIGGER, COUNT TO MOVE and THRESHOLD
Bar-locked sync keeps the motion in time with the song. It does not know anything about the part. A shaker that plays sixteenths for a bar and then rests still gets a pan sweeping through the silence, and when it comes back in it is wherever the lap has got to.
MODE has three settings: AUTO, which is the lap described above, TRIGGER and ENVELOPE. In TRIGGER the image only moves when told. It sits still until something happens, then steps to the next spot on the path.
What counts as "something happens" is set by two controls.
THRESHOLD is the level a hit has to cross to count. Set it above the bleed and ghost notes, and only the played hits register. Set it lower and quieter hits count too.
COUNT TO MOVE decides how many of those hits pass before the image moves. At one, every hit sends the part to a new spot. The store's example is a shaker or a hat set to move on every second hit, so the part dances around the kit in time with the player. Higher counts give fewer moves: the hat stays put for a phrase, then sits somewhere else for the next one.
Because the motion is driven by the playing, it stops when the playing stops. That is the behaviour of a part, not of an oscillator.
The trigger does not have to come from the track itself. Locomotion can take its hits from the input, the side chain, the MAN TRIG key or a MIDI note. A side chain from the kick or snare means a percussion loop changes position on the backbeat while its own busy pattern is ignored. A MIDI note lets you write the moves into a clip exactly where you want them. MAN TRIG moves the image to the next spot now and is automatable from the host, so a single move at the top of a chorus is one automation point.
The COUNT readout shows the hits toward the next move in TRIGGER mode, the lap's progress in AUTO, or the level in ENVELOPE. While you are setting THRESHOLD, watch it count: if it ticks on hits you cannot hear, raise THRESHOLD; if it misses hits you can, lower it.
In ENVELOPE, the third mode, the input's level pushes the image along the path. IMAGE FREEZE holds the image where it is, which parks the percussion for a breakdown.
Locomotion has 4 ms of latency, reported to the host, with bypass and MIX aligned, so switching it in or out does not shift the hits against the kit. DEPTH and IMAGE OFFSET decide how far the moves reach and where their middle sits: a shaker that belongs on the right of the kit wants OFFSET to the right and DEPTH well short of full.
What to try
Take a sixteenth-note shaker or hi-hat part and start a 14-day free trial of the full version. Load Locomotion as an insert, PATH on BOUNCE, MODE on TRIGGER and COUNT TO MOVE on two. Raise THRESHOLD until the COUNT readout ticks only on the hits you can hear, then pull DEPTH back until the moves sit inside the kit. Play it against the same part on AUTO, SYNC on at one bar, and decide which one sounds like the player and which one sounds like a machine.