Custom Curve Hand Accel Modulation

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Sensitivity transformations from physical acceleration

Hand Accel Modulation is an advanced tool for power users, allowing greater control over the curve response. Fundamentally, it allows the sensitivity transformations through the curve to respond differently when you are speeding up your hand than when you are slowing down. A regular acceleration curve responds only to the velocity of the mouse, not how it got there.

The physical acceleration of a human hand on a mouse is a transient — only while the hand is changing speed does the scaling apply.

What the plots show

• Acceleration curve: an example sensitivity curve is shown with a simulated flick movement, which is played back slowly for easy visualization. The movement begins accelerating slowly, then faster, then holds at a peak speed of 45 in/s, before slowing back down again in the same way.
  • when on Velocity Target: the curve shrinks or stretches to the left or right respectively, depending on the Scale parameter's sign.
  • when on Sensitivity Target: the whole curve lifts up or down, again depending on the Scale parameter's sign.

It is important to understand that this stretching or shrinking is not just a picture of the math, it is the math. Multiplying the velocity by a factor before the curve reads it, is the same as reading an unmodulated velocity against a curve compressed by that factor. This also explains why a static sensitivity (or a flat region of a curve) does not respond in Velocity mode: the compression moves the curve sideways, so a flat sensitivity is the same both modulated and unmodulated.

• Hand Accel Modulation scaling: this shows the internal function used to converge the physical acceleration with the input signal. It is plotted against the acceleration rather than time, so the whole shape of the transformation can be seen at once.

Parameters

• Scale & Limit: Scale decides how hard the hand has to be accelerating before much happens. It is how reactive the function is to your hand's physical acceleration. Limit sets the ceiling of the effect, which the response approaches but never quite reaches.
• Scale on: chooses whether the scaling happens when your hand is speeding up or slowing down.
• Velocity Target: multiplies the speed before the curve reads it. The output can only be a sensitivity the curve already contains, reached at a lower hand speed than usual. This means no sensitivity can be reached which isn't already defined by your curve.
• Sensitivity Target: multiplies the output after the curve has been read. The curve lifts instead of sliding, and sensitivities that are not contained in the curve can be transiently reached.

The Hand Accel meter reads the same in both because it is the same measurement either way — what differs is what that measurement is applied to.

Where it happens in the chain

The measurement is taken before the acceleration curve. On the Velocity target the scaling is applied to the speed at that point; on the Sensitivity target it is applied to the sensitivity the curve returns, so effectively stacks with it.

Two practical notes. The Scale value is affected by mouse DPI: it is recommended to state the DPI of each mouse on the Devices tab so that the acceleration is measured in real-world units, as per this visualization. Secondly, real mouse input is far too noisy to differentiate directly, so the driver smooths the speed before taking its rate of change — that is what Detection smoothing adjusts. The movement here is generated rather than measured, so there is nothing to smooth, and no such control on this page.

Some uses

These arise specifically with transient modulation and cannot be obtained only with a standard acceleration curve. The settings are given as Target, the sign of Scale, and Scale on.

• A wider window on the mouse pad for fast flicks. Velocity, negative Scale, on Acceleration. Dividing the velocity while the hand accelerates holds the sensitivity below what the curve alone would give, so a hard flick covers less screen for the same sweep of the pad. The flick can be thrown more aggressively, with additional margin before it overshoots.
• An increased sensitivity only when moving fast and accelerating together. Velocity, positive Scale, on Acceleration. Compressing the curve to the left brings its upper plateau within reach at a lower hand speed, but only while the hand is aggressively gaining speed. Preset 10, Modulated Jump is built this way, at Scale 1 and Limit 4 over a jump curve. This allows acceleration to be kept out of all movements besides extremely reactive 180° turns.
• Sensitivity transformation only while flicking. Sensitivity, positive Scale, on Acceleration. With the scaling landing after the curve, the curve itself can be left flat: all steady speeds are then unscaled and read as a single sensitivity, while a dynamic flick lifts it for as long as the transient lasts. Preset 17, Hand Accel Sensitivity Modulation does this at Scale 1 and Limit 2.5.
• Heavy smoothing without the “motion delay” it usually brings. Velocity, negative Scale, on Deceleration. Smoothing jittery mouse input increases sensitivity as you are slowing down your hand (since smoothing averages against previous values) — this is the so-called “motion delay” effect. Dividing the velocity into an acceleration curve while the hand slows down reduces sensitivity faster than the movement alone would, completely mitigating the downside while keeping the reduced jitter.
• Steadier sensitivity while tracking quickly left and right. Velocity, negative Scale, on Acceleration. Every direction change is a significant acceleration, so the division applies on each and holds the sensitivity where it would otherwise climb through an accel curve. This results in a dynamic “offset” in the curve that appears only under sharp physical acceleration, and is absent at a steady speed or with smoother hand accelerations.